Atomic Foundations of Matter (Matter ki Atomic Buniyaad): Class 9 Science Chapter 9 Hinglish mein

Exploration · Hinglish notes, simulations aur practice · Official NCERT chapter PDF ↗

Published 13 Oct 2026 · Updated 13 Oct 2026

95 min
1 simulation
37 practice questions
30 MCQs

Is chapter mein aap kya seekhenge

Tol kar dikhana ki physical aur chemical changes mein mass same rehta hai, aur samjhana ki yeh dikhne ke liye gas ko band karke rakhna kyun zaroori hai
Law of conservation of mass aur law of constant proportions se reactions aur compounds mein anjaan masses nikaalna
Dalton ke postulates batana aur unse chemical combination ke dono laws samjhana
Samjhana ki atoms electrons share karke (covalent bonds) ya transfer karke (ionic bonds) stable octet ya duplet tak kaise pahunchte hain, aur simple molecules aur ions ke dot-and-cross diagrams describe karna
Simple covalent aur ionic compounds ke naam rakhna aur valencies se unke formulae likhna, simplify karke aur polyatomic ions ke liye brackets use karke
Ionic aur covalent compounds ko solubility, electrical conductivity aur melting point ke basis par compare karna, aur yeh farak ions aur molecules ki madad se samjhana
Atomic masses se molecular masses aur formula unit masses calculate karna

NCERT Science Class 9, Chapter 9, pp. 162–183 par based original companion text. Yeh NCERT se juda nahi hai aur NCERT ne ise endorse nahi kiya hai.

Kya matter badalne par mass badalta hai?

Chapter 8, Journey Inside the Atom, tumhe atom ke andar le gaya tha: protons aur neutrons ka bana nucleus, aur uske chaaron taraf shells mein arranged electrons. Usne yeh bhi dikhaya ki atom sabse stable tab hota hai jab uske outermost shell mein aath electrons hon, ya do, agar woh shell pehla (K) shell ho. Yeh chapter wahin se shuru hota hai. Yeh poochta hai ki atoms ek doosre ko kaise pakad kar rakhte hain, jo woh banate hain use hum kaise likhte aur naam dete hain, aur ek reaction ke products ka weight kitna hota hai.

Shuruaat kitchen ki shelf se ek surprise ke saath karte hain. Sodium ek naram, chaandi jaisa chamakta metal hai jo paani ke saath zabardast reaction karta hai, aur chlorine ek dum ghotne wali, hari-peeli gas hai. Dono jud jaayein to sodium chloride ban jaata hai: har namak-daani mein rakha bilkul safe table salt. Compound ek bilkul naya substance hota hai jiski apni properties hoti hain; yeh uske elements ki properties ka mixture nahi hota. To ek seedha sa sawaal banta hai: jab ek substance doosre mein badalta hai, to kya matter ki total quantity badalti hai? Ek balance iska jawaab de sakta hai.

Activity 9.1NCERT Activity 9.1 · p. 163

Kya ghulne se weight badalta hai?

Tumhe chahiye

ek digital kitchen scale jo 0.1 g tak padhta ho
ek steel ka tumbler ya glass
paani
gur (jaggery) ka ek chhota tukda ya ek chammach cheeni
chalk ki ek stick aur ek kaagaz ki sheet

Pehle guess karo

Jab gur paani ke paas pan par rakha hai, scale ek reading dikhata hai. Gur ghul jaane ke baad reading hogi…

kam, kyunki gur gayab ho gayapehle jitni hizyada, kyunki ab paani mein gur hai

Khaali tumbler scale par rakho aur tare (ya zero) dabao, taaki display 0.0 g dikhaye.
Tumbler mein lagbhag aadha paani bharo. Gur ko tumbler ke paas kaagaz ke ek chhote square par rakho, pan par hi, aur reading note karo.
Gur ko paani mein daal do, kaagaz pan par hi rehne do. Tumbler ko uthaaye bina dheere-dheere ghumao, jab tak koi dalla na bache.
Reading phir se note karo.
Ab kaagaz ki sheet par rakhi chalk ki stick tolo. Usi kaagaz par use peeskar powder banao aur ek baar phir tolo.

Table 9.1

Change	Pehle ki reading (g)	Baad ki reading (g)
Gur ka ghulna
Chalk ko peesna

Tumhari entries apne aap save hoti hain.

Physical change mein har particle pan par hi rehta hai, isliye reading tiki rehti hai. Chemical change naye substances banata hai, aur unmein se kuch gases bhi ho sakte hain. Jab aisa hota hai, tab bhi kya balance same reading deta hai?

Activity 9.2NCERT Activity 9.2 · p. 163

Bottle mein jhaag: khuli ya band?

Tumhe chahiye

dhakkan ke saath 500 mL ki ek khaali fizzy-drink bottle
sirka (vinegar) ya nimbu ka ras
baking soda (sodium hydrogencarbonate)
steel ki ek chhoti katori
tissue paper aur dhaaga
ek digital scale

Pehle guess karo

Set-up A mein mixture ke jhaag banate waqt bottle khuli rehti hai. Final reading kya hogi?

Pehli reading se zyadaBilkul pehli reading jitniPehli reading se kam

Set-up A: bottle khuli chhodi
- Bottle mein lagbhag 3 cm gehraai tak sirka daalo. Chhoti katori mein chauthai teaspoon baking soda rakho. Bottle aur katori dono ko saath mein scale par rakho aur reading note karo.
- Soda ko bottle mein palat do aur khaali katori pan par hi rehne do. Jhaag banna band hone tak ruko, phir reading dobara note karo.
Set-up B: dhakkan band
- Bottle ko dho lo aur usi gehraai tak taaza sirka bharo. Utna hi soda tissue paper ki ek potli mein lapeto aur dhaage se baandh do.
- Potli ko bottle ki gardan ke andar latakne do, dhaage ka sira dhakkan ke neeche dabaa rahe, aur dhakkan kas kar band kar do. Band bottle ko tolo.
- Bottle uthao, ek baar ulta karo taaki sirka potli ko bhigo de, aur use wapas scale par rakh do. Jhaag banna band hone par reading note karo.

Table 9.2

Set-up	Pehli reading (g)	Aakhri reading (g)	Same ya alag?
A: khuli
B: dhakkan band

Tumhari entries apne aap save hoti hain.

Set-up A mein reading kuch tenths of a gram gir jaati hai. Set-up B mein band gas dhakkan par dabaav daalti hai aur bottle tight lagti hai, phir bhi reading nahi badalti. Jhaag carbon dioxide hai, reaction se bani ek gas. Khuli bottle se woh nikal gayi, isliye scale uska hisaab nahi rakh paaya; band bottle mein woh pan par hi rahi. Jab har product pan par rehta hai, to reaction ke baad ka total mass reaction se pehle ke total mass ke barabar hota hai. Isiliye khaali katori bhi pan par rehti hai: soda ke kuch daane usse chipke reh sakte hain.

Abhi nahi kar sakte? Simulation try karo · Fig. 9.2

4/4Gas bottle ke andar hi rehti hai: abhi bhi 158.9 g.

Fig. 9.1Jo gas nikal jaati hai woh tuli nahi jaati; jo band rehti hai woh tuli jaati hai.NCERT Fig. 9.2 · p. 164

Sirke ki ek plastic bottle digital kitchen scale par khadi hai. Pehle step mein bottle khuli hai aur uske paas baking soda ki ek chhoti katori rakhi hai; display 152.6 g padhta hai. Doosre step mein soda daal diya gaya hai, liquid bubbles se bhar gaya hai, arrows dikhate hain ki gas khuli gardan se nikal rahi hai aur display gir kar 152.1 g ho gaya hai, jis par lighter likha hai. Teesre step mein ek nayi bottle ka dhakkan band hai, aur gardan ke andar soda ki tissue potli latki hai; display 158.9 g padhta hai. Chauthe step mein potli sirke mein gir gayi hai, bubbles upar uthte hain, ek label kehta hai ki gas andar hi rehti hai, aur display abhi bhi 158.9 g padhta hai, jis par same likha hai.

Quick check

2 mein se 1

Agar khule container mein ho, to kaunsa change balance ki reading ko kam kar dega?

Glass mein barf ka pighalnaPaani mein cheeni ka ghulnaChalk ko peeskar powder bananaSirke mein baking soda ka jhaag banana

Answer dekho

Answer (D) Sirke mein baking soda ka jhaag banana

Jhaag ek gas hai, carbon dioxide, jo khule container se nikal jaati hai. Pighalna, ghulna aur peesna physical changes hain jinmein pan se kuch bahar nahi jaata.

9.1 Law of Conservation of Mass

Band bottle ek aisi baat dikhati hai jo ab tak naapi gayi har chemical reaction par laagu hoti hai. Sirka aur soda naye substances mein badal gaye, jinmein ek gas bhi thi, phir bhi pan par total mass fixed raha. Khuli bottle ne sirf mass khota hua dikhaya, kyunki ek product experiment se bahar chala gaya. French chemist Antoine Lavoisier saalon tak sealed glass vessels mein reactions tolne ke baad 1789 mein is nateeje par pahunche.

LawLaw of conservation of mass

Chemical reaction mein matter na banta hai na nasht hota hai: products ka total mass reactants ke total mass ke barabar hota hai.

Yeh law of conservation of mass (द्रव्यमान संरक्षण का नियम) hai. Yeh chemists ko hisaab rakhne ka ek powerful rule deta hai. Agar tumhe kisi reaction mein ek ko chhod kar baaki saare substances ke masses pata hain, to yeh law tumhe gayab wala mass bata deta hai.

Yahi idea tum particles ke level par bhi dekh sakte ho. Neeche ka simulation garam paani ka ek container dikhata hai. Dhakkan hata ho to tez chalte particles vapour ban kar nikal jaate hain, aur container mein bacha mass kam hota jaata hai. Dhakkan laga ho to har particle andar hi rehta hai, bilkul waise jaise gas band bottle ke andar rahi thi.

SimulationKhula ya band: particles kahan jaate hain?

Garam paani ka ek container jismein paani chalte particles ki tarah bana hai, saath mein ek thermometer, temperature slider aur lid switch. Dhakkan hata ho to tez particles surface chhod dete hain aur ek counter dikhata hai ki kitne nikal gaye aur kitne bache hain. Dhakkan laga ho to liquid chhodne wale particles dhakkan se takra kar wapas aa jaate hain, isliye escaped count badhna ruk jaata hai aur har particle container mein hi rehta hai.

Fig. 9.2Play dabao. Counter dikhata hai ki kitne particles container se nikal chuke hain.

Try karo

Dhakkan hata rehne do aur Play dabao. Lagbhag 20 seconds mein kitne particles nikalte hain?
Dhakkan laga do. Kya escaped counter ab bhi badhta hai? Yeh Activity 9.2 ke kis set-up jaisa hai?
Dhakkan hata kar temperature badhao. Ubalti dal ka khula bartan har minute halka kyun hota jaayega?

Activity 9.3NCERT Activity 9.3 · p. 165

Do saaf solutions, ek safed solid

Tumhe chahiye

do test tubes aur ek chhota beaker
dilute sodium sulfate solution
dilute barium chloride solution
ek balance jo 0.01 g tak padhta ho, agar tumhare school mein ho

Pehle guess karo

Dono solutions colourless hain. Jab unhe milaya jaata hai, to ek safed solid dikhta hai. Milane se pehle ki reading ki tulna mein, milane ke baad ki reading hogi…

zyada, kyunki ek solid bana haikam, kyunki liquids khatam ho gayesame, kyunki pan se kuch bahar nahi gaya

Do saaf test tubes par P aur Q likho aur unhe balance par rakhe chhote beaker mein khada karo. Tare dabao.
P mein lagbhag 5 mL sodium sulfate solution aur Q mein lagbhag 5 mL barium chloride solution daalo. Total reading note karo.
Q ka liquid P mein daal do. Tube Q ko wapas beaker mein rakho, aur P ko bhi wapas beaker mein khada karo.
Dekho P mein kya banta hai, phir reading dobara note karo.

Table 9.3

Kya record karna hai	Observation
Milane se pehle dono solutions kaise dikhte hain
Mixture kaisa dikhta hai
Pehle ki reading (g)
Baad ki reading (g)

Tumhari entries apne aap save hoti hain.

Activity 9.3 ki reaction ko hum word equation aur balanced chemical equation, dono tarah likh sakte hain. Chemical equation ke dono sides ke atoms gino: left ka har atom right mein bhi milta hai.

word equation

\begin{aligned} sodium sulfate + barium chloride \\ \to barium sulfate + sodium chloride \end{aligned}

(9.1)

N a_{2} S O_{4} + B a C l_{2} \overset{}{\to} B a S O_{4} + 2 N a C l

(9.2)

Example 9.1NCERT Example 9.1 · p. 166

Naape gaye masses se law ko check karna

School lab mein, stopper se band flask ke andar, 1.20 g magnesium ribbon ko aise dilute hydrochloric acid mein daala jaata hai jismein 3.65 g hydrogen chloride hai. Reaction khatam hone par flask mein 4.75 g magnesium chloride aur 0.10 g hydrogen gas hai. Kya yeh results law of conservation of mass ko follow karte hain?

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Example 9.2NCERT Example 9.2 · p. 166

Ek jaani-pehchaani reaction se scale up karna

Jab magnesium hawa mein jalta hai, to 24 g magnesium 16 g oxygen ke saath milkar 40 g magnesium oxide banata hai. Ek student 6.0 g magnesium poora jalata hai. Kitna magnesium oxide banta hai, aur kitni oxygen use hoti hai?

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Quick check

3 mein se 1

Ek candle balance par khadi hai aur das minute tak jalti hai. Reading kyun girti hai?

Wax jalne par mass nasht ho jaata haiWax aise products mein badalta hai jo hawa se halke hainFlame candle ko upar dhakelti haiJalne se bani gases kamre mein nikal jaati hain

Answer dekho

Answer (D) Jalne se bani gases kamre mein nikal jaati hain

Jalta wax carbon dioxide aur water vapour banata hai, jo ud jaate hain. Agar unhe band karke tola jaata, to total mass kam se kam utna hota jitna wax jala, kyunki hawa ki oxygen bhi ismein judti hai.

9.2 Law of Constant Proportions

Ab tak ki saari reactions mein baking soda, magnesium oxide aur sodium chloride jaise compounds the. Unke baare mein ek aur paina sawaal hai. Kya hydrogen aur oxygen kisi bhi amount mein milkar paani bana sakte hain, ek sample mein thodi zyada oxygen aur doosre mein thodi kam? Ya recipe fixed hai?

1790s mein French chemist Joseph Proust ne bahut alag-alag jagahon se ikattha kiye aur lab mein banaye gaye compounds ko analyse karke iska jawaab diya. Kisi compound ke har pure sample ki mass ke hisaab se banavat bilkul same thi. Carbon dioxide ke saath try karo. Teen bilkul alag jagahon se thodi-thodi lo: tumhari chhodi hui saans, sulagti koyle wali angithi aur soda bottle ka jhaag. Har sample ko purify karo aur uska 11 g analyse karo. Har ek se 3 g carbon aur 8 g oxygen milti hai. Pure paani bhi utna hi pakka hai: mass ke hisaab se hamesha ek hissa hydrogen aur aath hisse oxygen.

3/3Har sample mein mass ke hisaab se carbon : oxygen 3 : 8 hai.

Fig. 9.3Pure carbon dioxide ki mass ke hisaab se composition same hoti hai, chahe woh kahin se bhi aaye.NCERT Law of Constant Proportions · p. 167

Teen rows par breath, charcoal aur soda likha hai. Pehle step mein har row ek grey bar dikhati hai jis par 11 g carbon dioxide likha hai. Doosre step mein har bar ek chhote blue tukde mein, jis par 3 g carbon likha hai, aur ek lambe orange tukde mein, jis par 8 g oxygen likha hai, bat jaati hai. Teesre step mein neeche ek line par always 3 : 8 likha hai.

LawLaw of constant proportions

Kisi pure compound ke har sample ki mass ke hisaab se banavat same hoti hai: uske elements hamesha same ratio mein hote hain, chahe sample kahin se bhi aaya ho.

Yeh law of constant proportions (स्थिर अनुपात का नियम) hai. Ise law of definite proportions ya Proust's law bhi kaha jaata hai. Yeh compounds par laagu hota hai, mixtures par nahi: chai mein tum kitni bhi cheeni ghol sakte ho, lekin thodi extra oxygen ke saath paani nahi bana sakte.

Example 9.3NCERT Example 9.3 · p. 167

Fixed ratio ka use, kuch bach jaaye to

Iron sulfide ( $F e S$ ) mein iron aur sulfur hamesha 7 : 4 ke mass ratio mein hote hain. Ek student 14 g iron filings ko 10 g sulfur powder ke saath tab tak garam karta hai jab tak aur reaction nahi hoti. Kitna sulfur react karta hai, kitna bach jaata hai, aur kitna iron sulfide banta hai?

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Quick check

3 mein se 1

Pure carbon dioxide mein carbon aur oxygen ke masses hamesha 3 : 8 ke ratio mein hote hain. Jis sample mein 6 g carbon hai, usmein kitni oxygen hai?

8 g11 g16 g22 g

Answer dekho

Answer (C) 16 g

Double carbon matlab double oxygen:

6 = 2 \times 3

, isliye oxygen

= 2 \times 8 = 16

g. 22 g poore sample ka mass hai, oxygen ka nahi.

Practice · 6 questions

Ruko aur socho: answers ke saath

Short answerEasyPause and Ponder Q1
Aarti ke dauraan diye mein kapoor ka ek chhota tukda poora jal jaata hai aur kuch nahi chhodta. Kya isse pata chalta hai ki mass nasht ho sakta hai? Samjhao.
Solution dikhao
AnswerNahi. Kapoor oxygen ke saath react karke carbon dioxide aur water vapour banata hai, jo hawa mein nikal jaate hain.
Jalna kapoor aur hawa ki oxygen ke beech ek chemical reaction hai. Iske products, carbon dioxide aur water vapour, gases hain jo kamre mein mil jaati hain, isliye diya khaali dikhta hai. Agar saari gases ikattha karke toli ja sakti, to unka mass kapoor ke mass aur use hui oxygen ke mass ke jod ke barabar hota. Mass conserve hota hai; woh bas nazar se door chala gaya hai.
NumericalEasyPause and Ponder Q2
Magnesium ribbon ka 4.8 g ka tukda poora jalta hai, aur hawa ki 3.2 g oxygen use karta hai. Kitna safed magnesium oxide banta hai?
g
Answer dekho
Answer 8 g
Conservation of mass se, $4.8 + 3.2 = 8.0$ g magnesium oxide. Check: $4.8 : 3.2 = 3 : 2$ , jo $24 : 16$ ke barabar hai, isliye koi reactant nahi bachta.
NumericalMediumPause and Ponder Q3
Pure calcium carbonate, jisse chalk aur marble bante hain, mass ke hisaab se 40 % calcium hai. Pure calcium carbonate ke 25 g ke tukde mein kitna calcium hai?
g
Answer dekho
Answer 10 g
$\frac{40}{100} \times 25 = 10$ g calcium. Har pure sample mein yahi 40 % hota hai, chahe uska size ya source kuch bhi ho.
NumericalMediumPause and Ponder Q4
Ammonia mein nitrogen aur hydrogen 14 : 3 ke mass ratio mein jude hain. 28 g nitrogen ke saath kitna hydrogen judta hai, aur kitna ammonia banta hai?
Solution dikhao
Answer6 g hydrogen; 34 g ammonia.
$28 \div 14 = 2$ , isliye zaroori hydrogen $2 \times 3 = 6$ g hai. Conservation of mass se, bana ammonia $= 28 + 6 = 34$ g.
Short answerMediumPause and Ponder Q5
Law of constant proportions paani jaise compounds par kyun laagu hota hai, lekin nimbu paani jaise mixtures par kyun nahi?
Solution dikhao
AnswerCompound ki ek fixed recipe hoti hai jo uske atoms ke judne se tay hoti hai; mixture ke hisse kisi bhi amount mein ho sakte hain.
Compound mein elements ke atoms ek fixed number ratio mein jude hote hain, aur har tarah ke atom ka mass fixed hota hai, isliye mass ratio bhi fixed hota hai. Nimbu paani mein paani, nimbu ka ras, cheeni aur namak bas mile hue hain, chemically jude nahi. Tum zyada cheeni ya kam nimbu daal sakte ho, isliye har glass mein proportions badal jaate hain.
Short answerMediumPause and Ponder Q6
Magnesium oxide ke do samples analyse kiye jaate hain. Sample 1, jo chemical supplier se khareeda gaya, mein 3.0 g magnesium 2.0 g oxygen ke saath juda hai. Sample 2, jo school lab mein ribbon jala kar banaya gaya, mein 7.2 g magnesium 4.8 g oxygen ke saath juda hai. Kya yeh results law of constant proportions ko support karte hain?
Haan: dono ratios simplify hokar 3 : 2 bante hainNahi: sample 2 mein zyada magnesium haiNahi: oxygen ke masses alag hain
Answer dekho
Answer (A) Haan: dono ratios simplify hokar 3 : 2 bante hain
$3.0 : 2.0 = 3 : 2$ aur $7.2 : 4.8 = 3 : 2$ . Amounts alag hain, lekin proportion same hai, aur law bilkul yahi predict karta hai.

9.3 Dalton ki Atomic Theory

Dono laws batate hain ki kya hota hai; yeh nahi batate ki kyun. Products ka weight hamesha bilkul reactants jitna kyun hona chahiye? Paani kabhi 1 : 7 ya 1 : 9 kyun nahi hota? 1808 mein English teacher aur scientist John Dalton ne ek bold idea par bana jawaab diya: matter atoms naam ke chhote, na tootne wale particles se bana hai.

Dalton ne apni theory ko postulates (अभिधारणा) ke set ke roop mein rakha. Postulate ek basic idea hota hai jise theory apna starting point maanti hai. Use seedhe prove nahi kiya jaata; balki scientists usse nikalne wali predictions ko test karte hain, aur jab tak woh predictions experiments se match karti rehti hain, postulate tika rehta hai. Yeh rahe unke postulates, do groups mein.

Atoms ke baare mein
- Atoms woh chhote particles hain jinse saara matter bana hai, aur reaction mein asal mein yahi hissa lete hain.
- Koi bhi chemical reaction atom ko tod, bana ya nasht nahi kar sakti.
- Ek element ke saare atoms mass aur behaviour mein ek jaise hote hain, jabki alag elements ke atoms ke mass aur behaviour alag hote hain.
Compounds ke baare mein
- Compound banane ke liye atoms chhote whole-number ratios mein judte hain, jaise 1 : 1, 1 : 2 ya 2 : 3.
- Koi bhi particular compound hamesha same tarah ke atoms, same relative numbers mein rakhta hai.

Ab dono laws apne aap nikal aate hain. Reaction mein atoms bas alag hote hain aur naye partners ke saath judte hain, jaisa Fig. 9.4 dikhata hai. Koi atom na aata hai na gayab hota hai, aur har atom apna mass rakhta hai, isliye total mass badal nahi sakta. Yahi law of conservation of mass hai. Ab paani ke baare mein socho. Har water molecule mein do hydrogen atoms (har ek 1 u) aur ek oxygen atom (16 u) hota hai. Isliye har sample mein har 16 u oxygen ke liye 2 u hydrogen hota hai, yaani 1 : 8. Fixed masses wale atoms ke fixed numbers se fixed mass ratios milte hain: yahi law of constant proportions hai.

4/4Pehle chaar H aur do O atoms, baad mein bhi chaar H aur do O atoms: mass badal nahi sakta.

Fig. 9.4Reaction atoms ko naye groups mein jodti hai; woh unhe kabhi banati ya nasht nahi karti.

Atoms balls ki tarah bane hain: H likhi chhoti blue balls aur O likhi badi orange balls. Pehle step mein, left par, do hydrogen molecules hain, har ek H balls ka pair, aur ek oxygen molecule, O balls ka pair. Doosre step mein bonds tootne par har pair thoda alag hota hai. Teesre step mein atoms right ki taraf jaate hain aur do water molecules mein regroup hote hain, har ek mein ek O ball aur do H balls. Chauthe step mein neeche labels par before: 4 H, 2 O aur after: 4 H, 2 O likha hai.

9.4 Atoms Kaise Judte Hain

Atoms kam hi akele rehte hain. Do oxygen atoms jodi banakar oxygen molecule, $O_{2}$ , banate hain; hum jo hawa saans mein lete hain usmein oxygen isi form mein hoti hai. Isse shuruaat ka ek sawaal hal ho jaata hai: O ek akele oxygen atom ke liye hai, jabki $O_{2}$ do atoms wale molecule ke liye. Alag elements ke atoms bhi judte hain. Ek carbon atom aur do oxygen atoms milkar carbon dioxide, $C O_{2}$ , ka molecule banate hain, jo ek compound hai.

Definition

Molecule

Kisi substance ka sabse chhota particle jo akela exist kar sakta hai: do ya zyada jude hue atoms, jin par koi overall charge nahi hota, aur jo us substance ki properties dikhate hain.

Example $O_{2}$ ek element ka molecule hai; $C O_{2}$ ek compound ka molecule hai.

Kuch elements molecules bilkul nahi banate. Helium, neon aur argon ke outer shells pehle se full hote hain, isliye unke atoms akele hi stable hote hain aur yeh gases alag-alag atoms ke roop mein rehti hain. Isiliye argon garam filament ke saath react kiye bina electric bulb mein bhari ja sakti hai.

Zyadatar doosre atoms ka outer shell full nahi hota: usmein aath se kam electrons hote hain, ya do se kam jab K shell hi akela shell ho. Aisa atom do mein se kisi ek tarike se stable arrangement tak pahunch sakta hai:

doosre atom ke saath electrons share karke, taaki shared electrons dono atoms ke liye gine jaayein; ya
electrons transfer karke: ek atom ek ya zyada electrons de deta hai aur doosra atom unhe le leta hai.

Dono tarah, jude hue atoms ki energy alag rehne ke mukable kam ho jaati hai. Kam energy wala system zyada stable hota hai, bilkul jaise katori ki tali mein padi goli kinare par tiki goli se zyada tik kar rehti hai. Iske baad jo cheez atoms ko jode rakhti hai use chemical bond (रासायनिक आबंध) kehte hain.

Definition

Chemical bond

Itna strong attraction jo do atoms (ya ions) ko jode rakhe, taaki woh ek molecule ya compound ke hisson ki tarah kaam karein.

9.4.1 Electrons share karke bonding: covalent bond

Elements ke molecules

Sabse chhote atom se shuru karo. Hydrogen (atomic number 1) ke K shell mein ek hi electron hai, jabki usmein do ki jagah hai. Do hydrogen atoms milkar yeh masla hal karte hain: har ek apna electron ek shared pair mein daal deta hai jo dono nuclei ke beech rehta hai. Yeh pair dono atoms ke liye gina jaata hai, isliye ab har ek ke paas do electrons hain, yaani full K shell. Molecule ko jode kaun rakhta hai? Dono positive nuclei unke beech wale negative pair ki taraf kheenche jaate hain, isliye koi bhi atom door nahi ja sakta.

Definition

Covalent bond

Woh chemical bond jo tab banta hai jab do atoms electrons ka ek pair share karte hain, aam taur par har atom se ek electron aata hai.

ExampleHydrogen molecule ka bond, H–H.

Ek shared pair se bana bond single bond hota hai, jise ek line se banate hain: H–H. Chlorine (2, 8, 7) mein octet ke liye ek electron kam hai, isliye do chlorine atoms bhi ek pair share karte hain, Cl–Cl. Oxygen (2, 6) mein do kam hain. Isliye do oxygen atoms do pairs share karte hain, yaani double bond, jise O=O likhte hain. Nitrogen (2, 5) mein teen kam hain, isliye $N_{2}$ ke do atoms teen pairs share karte hain, yaani triple bond, N≡N. Fig. 9.5 ke steps dekho aur har atom ke aas-paas ke electrons gino: har molecule mein har atom ka shell full ho jaata hai.

4/5Oxygen atoms do pairs share karte hain: double bond.

Fig. 9.5Shared pairs wahan hote hain jahan outer shells overlap karte hain. Dots aur crosses sirf yeh dikhate hain ki har electron kahan se aaya; saare electrons ek jaise hote hain.NCERT Figs 9.6–9.8 · p. 169

Har atom ko uske outer shell ke circle ki tarah banaya gaya hai, andar uska symbol hai; ek atom ke electrons dots hain aur doosre atom ke crosses. Pehle step mein do hydrogen circles alag hain, har ek mein ek electron. Doosre step mein woh overlap karte hain aur dot aur cross overlap mein saath baithe hain, jis par H–H, one shared pair, single bond likha hai. Teesre step mein do chlorine circles ek shared pair ke saath overlap karte hain aur har atom par teen unshared pairs hain, jis par Cl–Cl likha hai. Chauthe step mein do oxygen circles do pairs share karte hain, har atom par do unshared pairs ke saath, jis par O=O, double bond likha hai. Paanchve step mein do nitrogen circles teen pairs share karte hain, har atom par ek unshared pair ke saath, jis par N≡N, triple bond likha hai.

Compounds ke molecules

Alag elements ke atoms bhi bilkul isi tarah electrons share karte hain. Hydrogen ko ek aur electron chahiye aur chlorine ko bhi, isliye hydrogen chloride mein woh ek pair share karte hain: H–Cl, ek single bond. Oxygen ko do electrons chahiye, lekin hydrogen atom sirf ek de sakta hai. Isliye oxygen atom do hydrogen atoms mein se har ek ke saath ek pair share karta hai, aur do single bonds ke saath paani, $H_{2} O$ , banta hai. Jis compound ke atoms shared electrons se jude hote hain, use covalent compound kehte hain.

Fig. 9.6 mein pattern dekho: har hydrogen atom ek kam electron ki kami poori karta hai. Nitrogen mein teen kam hain, isliye ammonia, $N H_{3}$ , mein woh teen hydrogen atoms se bond banata hai. Carbon mein chaar kam hain, isliye methane, $C H_{4}$ , mein woh chaar se bond banata hai; yahi gobar gas plant ki biogas ki main gas hai.

2/4Oxygen mein do kam hain: do hydrogens, do unshared pairs.

Fig. 9.6Hydrogen atoms ki sankhya utni hi hoti hai jitne electrons central atom ko octet ke liye kam padte hain.NCERT Figs 9.9–9.10 · p. 171

Beech mein central atom ke outer shell ka ek bada green circle hai; hydrogen atoms ke chhote blue circles usse overlap karte hain. Dots central atom ke electrons hain aur crosses hydrogen ke electrons. Pehle step mein central atom Cl hai, right par ek hydrogen aur teen unshared pairs; side note kehta hai ki Cl needs 1, so 1 hydrogen. Doosre step mein O hai, right aur neeche hydrogens aur do unshared pairs ke saath. Teesre step mein N hai, teen hydrogens aur ek unshared pair ke saath. Chauthe step mein C hai, chaaron taraf chaar hydrogens ke saath aur koi unshared pair nahi.

Real life meinNCERT Science aur Society ko Jodna · p. 171

Science aur society ko jodna: nucleus se energy

Chemical reactions sirf electrons ko rearrange karti hain; nuclei ko koi nahi chhoota. Nuclear reactions alag hain: jab uranium jaisa bhaari nucleus tootta hai, to woh per atom kisi bhi jalte fuel se laakhon guna zyada energy chhodta hai. India ka pehla nuclear power station 1969 mein Maharashtra ke Tarapur mein shuru hua, aur Tamil Nadu ke Kudankulam jaise plants ab koyla jalaye bina electricity banate hain. Homi J. Bhabha ne India ka atomic energy programme shuru kiya. Raja Ramanna, ek physicist jo baad mein Bhabha Atomic Research Centre aur Atomic Energy Commission ke head bane, ne dashakon tak desh ki nuclear research ko shape diya. Reactors mein radioactive banaye gaye substances cancer ke ilaaj aur medical equipment ko sterilise karne mein bhi use hote hain.

Covalent compounds ke naam rakhna

Kai covalent compounds sirf do non-metals se bane hote hain. Unke naam batate hain ki ek molecule mein har element ke kitne atoms hain, Greek se liye gaye number prefixes ki madad se.

Table 9.4Number prefixes

Atoms ki sankhya	Prefix
1	mono-
2	di-
3	tri-
4	tetra-
5	penta-
6	hexa-

Har element ko uske atoms ki sankhya ke hisaab se prefix do.
Exception: pehla element kabhi mono- nahi leta. Ek carbon aur ek oxygen se carbon monoxide banta hai, monocarbon monoxide nahi.
Doosre element ka ending badal kar -ide karo: oxygen se oxide, chlorine se chloride, sulfur se sulfide.
Jab a ya o par khatam hone wala prefix kisi vowel se takraata hai, to uska aakhri letter hat jaata hai, isliye mono- + oxide ko monoxide likhte hain. i par khatam hone wala prefix use rakhta hai, jaise trioxide mein.
Jis compound ka formula hydrogen se shuru hota hai, usmein hydrogen ko koi prefix nahi milta.

$N O$ : nitrogen monoxide
$S O_{2}$ : sulfur dioxide, aur $S O_{3}$ : sulfur trioxide
$C C l_{4}$ : carbon tetrachloride
$P C l_{5}$ : phosphorus pentachloride
$N_{2} O$ : dinitrogen monoxide, woh 'laughing gas' jo kabhi dentists ke clinics mein aam thi
$H C l$ : hydrogen chloride, aur $H_{2} S$ : hydrogen sulfide (hydrogen pehle hai, isliye koi prefix nahi)

Kuch compounds roz ke naamon se jaane jaate hain jo tumhe hamesha use karne chahiye: water, $H_{2} O$ ; ammonia, $N H_{3}$ ; aur methane, $C H_{4}$ .

Quick check

3 mein se 1

Oxygen molecule ke do atoms ke beech kitne electrons share hote hain?

2468

Answer dekho

Answer (B) 4

Double bond do shared pairs hota hai, yaani chaar electrons. Aath woh sankhya hai jo shared electrons milakar har oxygen atom ke aas-paas aakhir mein hoti hai.

Practice · 4 questions

Ruko aur socho: answers ke saath

DiagramMediumPause and Ponder Q8
Bromine (atomic number 35) ke outermost shell mein saat electrons hain aur yeh $B r_{2}$ molecules ke roop mein rehta hai. $B r_{2}$ ka dot-and-cross diagram describe karo aur bond ka type batao.
Solution dikhao
AnswerEk shared pair (single covalent bond, Br–Br) aur har atom par teen unshared pairs.
Har bromine atom ke 7 outer electrons hain aur use 1 aur chahiye. Har atom ek electron shared pair mein daalta hai, isliye ab har ek ke 8 outer electrons gine jaate hain: 2 shared pair mein aur 6 teen unshared pairs mein. Do overlapping circles banao, overlap mein ek dot aur ek cross, aur har atom ki bahar wali side par dots (ya crosses) ke teen pairs. Ek shared pair ek single covalent bond hai, Br–Br.
DiagramMediumPause and Ponder Q9
Fluorine ka atomic number 9 hai. Samjhao ki hydrogen fluoride, $H F$ , ke molecule mein hydrogen atom aur fluorine atom stable shells tak kaise pahunchte hain.
Solution dikhao
AnswerWoh ek pair share karte hain: H ko full K shell (2) milta hai, F ko octet (8). Single bond, H–F.
Fluorine 2, 7 hai, isliye octet ke liye usmein ek electron kam hai; hydrogen mein full K shell ke liye ek kam hai. Har ek shared pair ko ek electron deta hai. Ab hydrogen ke aas-paas 2 electrons hain, aur fluorine ke paas 8 (shared pair plus teen unshared pairs). Yeh ek shared pair ek single covalent bond hai, H–F.
10
DiagramHardPause and Ponder Q10
Dikhao ki har molecule mein electrons kaise share hote hain.
1. Carbon disulfide, $C S_{2}$ (carbon 2, 4; sulfur 2, 8, 6)
  Solution dikhao
  AnswerS=C=S: do double bonds.
  Carbon ko 4 electrons chahiye aur har sulfur ko 2. Carbon har sulfur atom ke saath do pairs share karta hai, jisse do double bonds bante hain, S=C=S. Tab carbon ke 8 electrons gine jaate hain (chaar shared pairs) aur har sulfur ke 8 (do shared pairs plus do unshared pairs). Carbon dioxide, O=C=O, bhi isi tarah bana hai.
2. Phosphine, $P H_{3}$ (phosphorus ka atomic number 15 hai)
  Solution dikhao
  AnswerTeen P–H single bonds aur P par ek unshared pair.
  Phosphorus 2, 8, 5 hai, isliye nitrogen ki tarah usmein octet ke liye teen kam hain. Woh teen hydrogen atoms mein se har ek ke saath ek pair share karta hai. Aakhir mein phosphorus ke paas teen shared pairs aur ek unshared pair, yaani 8 electrons hote hain; har hydrogen ke paas 2.
Short answerEasyPause and Ponder Q11
Ek bulb mein argon (atomic number 18) bhari hai. Argon metal filament ke saath electrons na share kyun karta hai na transfer?
Solution dikhao
AnswerArgon 2, 8, 8 hai: uska outer shell pehle se full hai, isliye bonding se use kuch nahi milta.
Argon ke electrons 2, 8, 8 arranged hain, isliye uske outermost shell mein pehle se stable octet hai. Electrons share karne, khone ya paane se woh aur stable nahi hoga, isliye argon atoms akele aur unreactive rehte hain. Isiliye bulbs mein yahi bhari jaati hai.

9.4.2 Electron transfer se bonding: ionic bond

Full shell tak pahunchne ka raasta sirf sharing nahi hai. Jis atom ke outer shell mein sirf ek, do ya teen electrons hon, use aam taur par paanch ya zyada extra electrons ikattha karne ke bajaye unhe de dena aasaan lagta hai. Jis atom ke paanch, chhe ya saat outer electrons hon, woh aksar kam pade kuch electrons le leta hai, ya share karta hai. Pehle 18 elements mein lithium, sodium, magnesium aur aluminium aise typical dene wale hain. Chapter 8 ki electron arrangements wali table mein tum aur kaun se dhoondh sakte ho?

Sodium (atomic number 11) lo, jo 2, 8, 1 arranged hai. Agar woh apna akela outer electron kho de, to neeche ka aath wala full shell uska outer shell ban jaata hai. Lekin ab uske paas 11 protons aur sirf 10 electrons hain, isliye us par positive charge ki ek unit hai. Yeh charged particle sodium ion hai, jise $N a^{+}$ likhte hain. Positive charge wale ion ko cation (धनायन) kehte hain.

sodium ek electron khota hai

N a \overset{}{\to} N a^{+} + e^{-}

(9.3)

Chlorine (2, 8, 7) iska ulta karta hai. Woh ek electron leta hai aur apna octet poora karta hai, jisse 17 protons aur 18 electrons ho jaate hain: negative charge ki ek unit. Yeh chloride ion, $C l^{-}$ , hai, aur negative charge wale ion ko anion (ऋणायन) kehte hain. Cations aur anions ko milakar ions (आयन) kehte hain.

chlorine ek electron leta hai

C l + e^{-} \overset{}{\to} C l^{-}

(9.4)

3/4Ab $N a^{+}$ (2, 8) aur $C l^{-}$ (2, 8, 8): dono ke octets hain.

Fig. 9.7Pehle transfer, phir attraction: sodium ek electron deta hai, chlorine use leta hai, aur opposite charge wale ions jude rehte hain.NCERT Figs 9.11–9.13 · p. 172

Do atoms bane hain, unke electron shells rings ki tarah aur electrons dots ki tarah: left mein 2, 8, 1 electrons wala sodium aur right mein 2, 8, 7 wala chlorine. Sodium ka akela outer electron ek khule circle ki tarah bana hai. Doosre step mein 1 electron likha ek dashed arrow use chlorine ke outer ring ki khaali jagah tak le jaata hai. Teesre step mein sodium ka khaali outer ring gayab ho gaya hai aur dono atoms ions ke roop mein square brackets mein hain: sodium ion, 2, 8, plus charge ke saath, aur chloride ion, 2, 8, 8, minus charge ke saath. Chauthe step mein ions attract likhe double-headed arrow ke saath paas aate hain, aur neeche ionic bond shabd dikhte hain.

Opposite charges attract karte hain. Jab sodium apna electron chlorine ko de deta hai, to $N a^{+}$ aur $C l^{-}$ ions ek doosre ko zor se kheenchte hain, aur sodium chloride banta hai. Yeh attraction ionic bond (आयनिक आबंध) hai, aur is tarah jude compound ko ionic compound kehte hain.

Definition

Ionic bond

Opposite charge wale ions ke beech ka kheenchav, yaani electrostatic attraction, jo unhe ionic compound mein jode rakhta hai.

ExampleCommon salt mein $N a^{+}$ aur $C l^{-}$ ions ke beech ka attraction.

2/3Ions checkerboard ki tarah repeat hote hain: har padosi ka charge opposite hota hai.

Fig. 9.8Crystal ki ek layer. Har sodium ion apni layer mein chaar chloride ions ko chhoota hai, plus ek upar aur ek neeche: kul chhe.NCERT Fig. 9.14 · p. 173

Plus likhe chhote blue circles sodium ions hain aur minus likhe bade green circles chloride ions. Pehle step mein sirf ek sodium ion aur ek chloride ion aas-paas dikhaye gaye hain. Doosre step mein poori layer dikhti hai, saat ions aar-paar aur paanch neeche, plus aur minus checkerboard ki tarah baari-baari se. Teesre step mein baaki ions dhundhle ho jaate hain, aur ek dashed square beech wale sodium ion ko layer mein uske chaar chloride padosiyon se jodta hai.

Kuch atoms do electrons transfer karte hain. Magnesium (2, 8, 2) do electrons de deta hai aur $M g^{2 +}$ ban jaata hai. Oxygen (2, 6) aur sulfur (2, 8, 6) do-do electrons lete hain aur oxide ion, $O^{2 -}$ , aur sulfide ion, $S^{2 -}$ , ban jaate hain. Lekin chlorine atom sirf ek electron le sakta hai. Isliye jab magnesium chlorine se milta hai, to magnesium ke do electrons lene ke liye do chlorine atoms chahiye, aur compound $M g C l_{2}$ banta hai: har do $C l^{-}$ ions ke liye ek $M g^{2 +}$ ion (Fig. 9.9).

3/3Ek $M g^{2 +}$ aur do $C l^{-}$ : formula $M g C l_{2}$ hai.

Fig. 9.9Ek magnesium atom ko apne do outer electrons dene ke liye do chlorine atoms chahiye.

Sirf outer shells bane hain. Beech mein magnesium ke circle mein do dots hain; dono taraf ek-ek chlorine circle mein saat crosses hain. Doosre step mein dashed arrows magnesium ka ek electron har chlorine atom tak le jaate hain. Teesre step mein square brackets teenon ions ko gherte hain, magnesium ka shell dhundhla ho jaata hai, aur electron arrangements badal kar magnesium ke liye 2, 8 aur har chlorine ke liye 2, 8, 8 ho jaate hain; charge labels 2 plus charge wala ek magnesium ion aur minus charge wale do chloride ions dikhate hain, aur neeche formula MgCl2 dikhta hai.

Ionic compounds ke naam rakhna

Ionic compound ka naam ek jodi ki tarah padha jaata hai: pehle cation, phir anion. Kyunki metals aksar electrons khote hain aur non-metals aksar electrons lete hain, isliye pehla shabd aam taur par metal hota hai aur doosra ek non-metal jiska ending badal kar -ide ho gaya ho. Kuch toothpastes mein sodium fluoride hota hai, sunscreens mein aksar zinc oxide hota hai, aur purani black-and-white films mein silver bromide use hota tha. Cation bas apne element ka naam rakhta hai.

Kuch ions aapas mein bonded atoms ke groups hote hain jo ek unit ki tarah ghoomte hain aur ek overall charge rakhte hain. Yeh polyatomic ions hain, jaise sulfate, $S O_{4}^{2 -}$ , aur ammonium, $N H_{4}^{+}$ , jo sabse common positive wala hai. Zyadatar polyatomic anions ke naam -ide nahi, -ate par khatam hote hain; hydroxide, $O H^{-}$ , jaana-pehchaana exception hai.

Ion par charge ka size uski valency (संयोजकता) hai, yaani atom ya group ki combining capacity. Iron aur copper dono do alag ions bana sakte hain, isliye unke naamon par label hota hai: ferrous ( $F e^{2 +}$ ) aur ferric ( $F e^{3 +}$ ), cuprous ( $C u^{+}$ ) aur cupric ( $C u^{2 +}$ ). Neeche ki do tables, valency ke hisaab se grouped, is chapter mein use hone wale ions dikhati hain.

Table 9.5Common cations, valency ke hisaab se

Valency	Cations
1	sodium $N a^{+}$ , potassium $K^{+}$ , lithium $L i^{+}$ , silver $A g^{+}$ , cuprous $C u^{+}$ , ammonium $N H_{4}^{+}$
2	magnesium $M g^{2 +}$ , calcium $C a^{2 +}$ , barium $B a^{2 +}$ , zinc $Z n^{2 +}$ , ferrous $F e^{2 +}$ , cupric $C u^{2 +}$
3	aluminium $A l^{3 +}$ , ferric $F e^{3 +}$

Table 9.6Common anions, valency ke hisaab se (polyatomic wale hain: cations mein ammonium, aur yahan hydroxide, nitrate, hydrogencarbonate, carbonate, sulfate aur phosphate)

Valency	Anions
1	fluoride $F^{-}$ , chloride $C l^{-}$ , bromide $B r^{-}$ , iodide $I^{-}$ , hydroxide $O H^{-}$ , nitrate $N O_{3}^{-}$ , hydrogencarbonate $H C O_{3}^{-}$
2	oxide $O^{2 -}$ , sulfide $S^{2 -}$ , carbonate $C O_{3}^{2 -}$ , sulfate $S O_{4}^{2 -}$
3	nitride $N^{3 -}$ , phosphate $P O_{4}^{3 -}$

Quick check

4 mein se 1

Aluminium 2, 8, 3 arranged hai. Aluminium atom kaunsa ion banata hai?

A l^{+}

, ek electron kho kar

A l^{3 -}

, teen electrons le kar

A l^{5 -}

, paanch electrons le kar

A l^{3 +}

, teen electrons kho kar

Answer dekho

Answer (D) $A l^{3 +}$ , teen electrons kho kar

Teen electrons khone se full 2, 8 arrangement bachta hai aur 10 electrons ke mukable 13 protons: yaani 3+ charge. Paanch lena kahin zyada mushkil hota, aur electron khone se ion hamesha positive banta hai, kabhi negative nahi.

Practice · 4 questions

Ruko aur socho: answers ke saath

Short answerEasyPause and Ponder Q12
Fluorine ka atomic number 9 hai. Fluorine atom kaunsa ion banata hai, aur kaise?
Solution dikhao
AnswerFluoride ion, $F^{-}$ , ek electron le kar.
Fluorine 2, 7 hai, octet se ek electron kam. Woh ek electron le kar 2, 8 ban jaata hai. 9 protons aur 10 electrons ke saath us par ek negative charge hota hai: yahi fluoride ion, $F^{-}$ , hai.
Quick answerMediumPause and Ponder Q13
Aluminium atom $A l^{3 +}$ banne ke liye electrons de deta hai. Oxygen atom $O^{2 -}$ banne ke liye electrons leta hai. Isliye aluminium oxide mein aluminium ions oxide ions ke saath judte hain.
Answer dekho
Answer (1) 3, (2) 2, (3) 2, (4) 3
Do Al atoms $2 \times 3 = 6$ electrons dete hain aur teen O atoms $3 \times 2 = 6$ lete hain, isliye formula $A l_{2} O_{3}$ hai.
14
DiagramMediumPause and Ponder Q14
Electron arrangements se dikhao ki har metal apna cation aur phir apna fluoride kaise banata hai.
1. Lithium (atomic number 3)
  Solution dikhao
  Answer $L i$ (2, 1) → $L i^{+}$ (2); fluoride $L i F$ .
  Lithium (2, 1) apna ek outer electron kho kar $L i^{+}$ ban jaata hai, jo 2 arranged hai. Fluorine atom (2, 7) woh electron le kar $F^{-}$ (2, 8) ban jaata hai. Ek $L i^{+}$ ek $F^{-}$ ko balance karta hai, isliye lithium fluoride $L i F$ hai.
2. Magnesium (atomic number 12)
  Solution dikhao
  Answer $M g$ (2, 8, 2) → $M g^{2 +}$ (2, 8); fluoride $M g F_{2}$ .
  Magnesium (2, 8, 2) do electrons kho kar $M g^{2 +}$ (2, 8) ban jaata hai. Har fluorine atom sirf ek le sakta hai, isliye do fluorine atoms chahiye, jisse do $F^{-}$ ions bante hain. Magnesium fluoride $M g F_{2}$ hai.
Short answerMediumPause and Ponder Q15
Samjhao ki potassium atoms (2, 8, 8, 1) aur ek oxygen atom (2, 6) se potassium oxide, $K_{2} O$ , kaise banta hai.
Solution dikhao
AnswerDo K atoms mein se har ek, ek O atom ko ek electron deta hai: do $K^{+}$ ions aur ek $O^{2 -}$ ion.
Har potassium atom apna akela outer electron kho kar $K^{+}$ (2, 8, 8) ban jaata hai. Oxygen atom ko octet poora karne ke liye do electrons chahiye, isliye woh do potassium atoms se ek-ek le kar $O^{2 -}$ (2, 8) ban jaata hai. Do $K^{+}$ ions aur ek $O^{2 -}$ ion ek doosre ko attract karte hain, aur charges balance ho jaate hain: $2 \times (+ 1) + (- 2) = 0$ .

9.5 Chemical Formulae Likhna

Chemical formula (रासायनिक सूत्र) symbols aur subscripts naam ke chhote numbers ki madad se dikhata hai ki compound mein kaun se elements hain aur kis proportion mein. $H_{2} O$ mein subscript 2 hydrogen ka hai, aur oxygen ka na likha subscript 1 hai. Tum har formula electrons bana kar nikaal sakte ho, jaise Section 9.4 mein, lekin valencies se kahin jaldi raasta milta hai.

9.5.1 Covalent compounds ke chemical formulae likhna

Covalent compound mein kisi element ki valency utni hoti hai jitne electrons uska har atom share karta hai, aur yahi uske banaye bonds ki sankhya bhi hai. Common values hain: hydrogen aur chlorine ke liye 1, oxygen aur sulfur ke liye 2, nitrogen ke liye 3 aur carbon ke liye 4. Phir yeh chaar steps follow karo:

Elements ke symbols paas-paas likho.
Har element ki valency uske symbol ke neeche likho.
Valencies ko cross karo, taaki har number doosre symbol ka subscript ban jaaye.
Dono subscripts ko kisi bhi common factor se divide karo, aur 1 ka subscript mat likho.

Table 9.7Valencies se covalent compounds ke formulae

Elements	Valencies	Cross karne ke baad	Formula
hydrogen, oxygen	1, 2	$H_{2} O_{1}$	$H_{2} O$
nitrogen, hydrogen	3, 1	$N_{1} H_{3}$	$N H_{3}$
carbon, oxygen	4, 2	$C_{2} O_{4}$	$C O_{2}$ (2 se divide karo)

Har result ko Fig. 9.5 aur Fig. 9.6 mein gine bonds se check karo: water mein do O–H bonds hain, ammonia mein teen N–H bonds, aur carbon dioxide mein do double bonds.

9.5.2 Ionic compounds ke chemical formulae likhna

Ionic compound ke liye har ion ki valency uske charge ka size hoti hai, aur steps lagbhag same hain:

Pehle cation ka symbol likho, phir anion ka.
Har ion ka charge number uske symbol ke neeche likho.
Numbers ko cross karke subscripts bana do.
Kisi bhi common factor se divide karo, kyunki ionic compound ka formula uske ions ka sabse simple whole-number ratio dikhata hai.
Agar koi polyatomic ion ek se zyada baar chahiye, to use brackets mein rakho aur subscript bahar likho.
Final formula mein charges mat likho.

4/4 $A l_{2} S_{3}$ : 3+ ke do ions aur 2− ke teen ions se $+ 6 - 6 = 0$ milta hai.

Fig. 9.10Har ion ka charge number doosre ion ka subscript ban jaata hai.NCERT 9.5.2 Examples · p. 176

Symbols Al aur S bade likhe hain, unke upar naam aluminium aur sulfide hain. Doosre step mein unke charges, 3 plus aur 2 minus, neeche dikhte hain. Teesre step mein ek rangeen 3, Al ke neeche se dashed crossing arrows ke saath S ke neeche-right tak jaata hai, aur ek rangeen 2, S ke neeche se Al ke neeche-right tak jaata hai. Chauthe step mein formula Al2S3 ek box mein dikhta hai, neeche ek check ke saath: 2 times plus 3 aur 3 times minus 2 milakar total 0.

Ions koi bhi hon, test same hai: positive charges ko negative charges cancel karne chahiye, kyunki poora compound neutral hota hai. Table yeh method ions ke chhe pairs par dikhati hai, jinmein woh do situations bhi hain jinmein extra dhyaan chahiye: simplify karna aur brackets.

Table 9.8Criss-cross karke ionic compounds ke formulae

Ions	Cross karne ke baad	Formula	Kyun
$B a^{2 +}$ , $C l^{-}$	$B a_{1} C l_{2}$	$B a C l_{2}$	1 ka subscript nahi likhte
$Z n^{2 +}$ , $O^{2 -}$	$Z n_{2} O_{2}$	$Z n O$	2 se divide karo
$K^{+}$ , $S O_{4}^{2 -}$	$K_{2} (S O_{4})_{1}$	$K_{2} S O_{4}$	ek sulfate ion: brackets nahi
$C a^{2 +}$ , $O H^{-}$	$C a_{1} (O H)_{2}$	$C a (O H)_{2}$	do hydroxide ions: brackets
$N H_{4}^{+}$ , $C O_{3}^{2 -}$	$(N H_{4})_{2} (C O_{3})_{1}$	$(N H_{4})_{2} C O_{3}$	do ammonium ions: brackets
$A l^{3 +}$ , $P O_{4}^{3 -}$	$A l_{3} (P O_{4})_{3}$	$A l P O_{4}$	3 se divide karo

Do galtiyan aam hain. Calcium hydroxide $C a (O H)_{2}$ hai, $C a O H_{2}$ nahi: brackets ke bina 2 sirf hydrogen ko double karta. Aur charges kabhi final formula mein nahi aate. Jaise barium chloride mein tum sirf $B a C l_{2}$ likhte ho. Section 9.8 ke formula builder mein tum ions ka koi bhi pair khud try kar sakte ho.

Practice · 3 questions

Ruko aur socho: answers ke saath

16
Quick answerEasyPause and Ponder Q16
Har covalent compound ka naam batao.
1. $S i O_{2}$ :
  Answer dekho
  Answer silicon dioxide
  Ek silicon (mono- nahi), do oxygens: silicon dioxide, jo ret ka main substance hai.
2. $N_{2} O_{3}$ :
  Answer dekho
  Answer dinitrogen trioxide
  Do nitrogens (di-) aur teen oxygens (tri-): dinitrogen trioxide.
3. $P B r_{3}$ :
  Answer dekho
  Answer phosphorus tribromide
  Ek phosphorus, teen bromines: phosphorus tribromide.
4. $S F_{4}$ :
  Answer dekho
  Answer sulfur tetrafluoride
  Ek sulfur, chaar fluorines: sulfur tetrafluoride.
17
Short answerMediumPause and Ponder Q17
Har compound ka formula likho.
1. calcium hydrogencarbonate
  Solution dikhao
  Answer $C a (H C O_{3})_{2}$
  $C a^{2 +}$ aur $H C O_{3}^{-}$ cross hokar 1 : 2 dete hain. Polyatomic ion do baar aata hai, isliye woh brackets mein jaata hai: $C a (H C O_{3})_{2}$ .
2. nitrogen trichloride
  Solution dikhao
  Answer $N C l_{3}$
  Naam khud ek nitrogen aur teen chlorines batata hai (valencies 3 aur 1): $N C l_{3}$ .
3. ferrous sulfide
  Solution dikhao
  Answer $F e S$
  Ferrous $F e^{2 +}$ hai aur sulfide $S^{2 -}$ . Cross karne se $F e_{2} S_{2}$ milta hai, jo simplify hokar $F e S$ banta hai.
4. cupric nitrate
  Solution dikhao
  Answer $C u (N O_{3})_{2}$
  Cupric $C u^{2 +}$ hai aur nitrate $N O_{3}^{-}$ , isliye ek copper ion ko do nitrate ions chahiye, brackets mein: $C u (N O_{3})_{2}$ .
18
Short answerMediumPause and Ponder Q18
Ions ke har pair se bane compound ka formula likho.
1. $B a^{2 +}$ aur $O H^{-}$
  Solution dikhao
  Answer $B a (O H)_{2}$
  Charges 2 aur 1 cross hokar $B a_{1} (O H)_{2}$ dete hain; do hydroxide ions ko brackets chahiye: $B a (O H)_{2}$ , barium hydroxide.
2. $N H_{4}^{+}$ aur $P O_{4}^{3 -}$
  Solution dikhao
  Answer $(N H_{4})_{3} P O_{4}$
  Charges 1 aur 3 cross hokar teen ammonium ions aur ek phosphate ion dete hain. Ammonium polyatomic hai aur teen baar aata hai, isliye woh brackets mein hai: $(N H_{4})_{3} P O_{4}$ , ammonium phosphate.

9.6 Ionic aur Covalent Compounds ki Properties

Ionic compounds ions se bane hote hain, aur covalent compounds molecules se. Kya yeh farak unke behaviour mein dikhta hai? Activity 9.4 do roz ki properties test karti hai: substance ghulta hai ya nahi, aur woh electric current ko jaane deta hai ya nahi.

Activity 9.4NCERT Activity 9.4 · p. 177

Ghol do, phir bulb se test karo

Tumhe chahiye

common salt, washing soda, cheeni, kapoor aur candle-wax ki chhilan ke chhote samples
paani aur kerosene
stand mein das test tubes
ek conductivity tester: 9 V battery, chhota torch bulb, wires, aur card ke tukde mein ghusaayi do pencil leads

Pehle guess karo

Tumhe kya lagta hai, paani mein daalne ke baad kaunsa sample bulb jalayega?

CheeniCommon saltCandle waxKapoor

A. Kya yeh ghulta hai?
- Har sample ki ek chutki paani wali test tube mein daalo, aur ek aur chutki kerosene wali test tube mein.
- Har tube ko ek minute tak dheere se hilao aur note karo ki sample gayab hota hai ya nahi.
B. Kya yeh conduct karta hai?
- Tester ki dono pencil leads ko har solid sample ke sookhe dher mein dabao. Kya bulb jalta hai?
- Leads ko part A ke har sample ke paani mein, ek-ek karke, dubao. Samples ke beech leads ko dho kar ponch lo.
- Ek jaisa behave karne wale samples ko group karo.

Table 9.9

Sample	Paani mein ghulta hai?	Kerosene mein ghulta hai?	Bulb jalta hai: sookha solid?	Bulb jalta hai: paani mein?
Common salt
Washing soda
Cheeni
Kapoor
Candle wax

Tumhari entries apne aap save hoti hain.

Namak aur washing soda paani mein ghulte hain lekin kerosene mein nahi, aur unke solutions bulb jalate hain, jabki sookhe crystals nahi jalate. Kapoor aur wax paani mein mushkil se ghulte hain lekin kerosene mein ghul jaate hain, aur woh kabhi bulb nahi jalate. Cheeni paani mein ghulti hai, phir bhi uska solution bulb ko band hi rakhta hai. Paani mein conduct karne wale dono ionic compounds hain; cheeni, kapoor aur wax covalent compounds hain.

2/3Free ions opposite charge wali rods ki taraf jaate hain: bulb jalta hai.

Fig. 9.11Liquid mein current sirf chalte hue ions le jaate hain.NCERT Fig. 9.15 · p. 178

Upar left mein ek battery aur upar right mein ek bulb, beaker mein dubi do rods se wire se jude hain; left rod par minus aur right rod par plus likha hai. Pehle step mein beaker mein sirf sookhe salt crystals hain aur bulb off hai. Doosre step mein beaker mein salt solution hai jismein plus ions aur minus ions phaile hain; plus ions minus rod ki taraf aur minus ions plus rod ki taraf khisak gaye hain, aur bulb chaaron taraf rays ke saath jalta hai. Teesre step mein beaker mein sugar solution hai jismein bina charge wale sugar molecules hain, jin par no charge likha hai, aur bulb off hai.

Yeh farak kyun? Electric current charge ka behna hai. Salt solution mein $N a^{+}$ aur $C l^{-}$ ions ghoomne ke liye free hote hain, cations negative rod ki taraf aur anions positive rod ki taraf, aur yahi movement current le jaata hai. Sookhe crystal mein har ion lattice mein apne padosiyon ki pakad mein hota hai aur sirf apni jagah par hil sakta hai, isliye koi charge nahi behta aur bulb band rehta hai. Cheeni bina charge wale poore molecules ke roop mein ghulti hai, isliye uska solution bhi current nahi le ja sakta. Kapoor aur wax bhi koi ions nahi dete.

Agar ionic compound ko ghola nahi, pighlaya jaaye to? Pighalne se bhi ions lattice se free ho jaate hain, isliye pighla hua sodium chloride electricity conduct karta hai. Pighla hua covalent substance, jaise liquid wax, mein phir bhi ions nahi hote aur woh conduct nahi karta.

Water molecules ions ki taraf attract hote hain aur unhe ek-ek karke crystal se kheench kar nikaal sakte hain, isiliye kai ionic compounds paani mein ghul jaate hain. Wax aur kapoor jaise covalent substances chemically kerosene jaise zyada hain aur uske saath mil jaate hain. Zor se attract karne wale ions ki lattice todne mein bahut zyada energy lagti hai, isliye ionic compounds sirf high temperatures par pighalte hain: sodium chloride 801 °C par pighalta hai. Zyadatar covalent compounds ke molecules ek doosre ko kahin kamzor attract karte hain, isliye naphthalene lagbhag 80 °C par aur candle wax lagbhag 60 °C par pighal jaata hai.

Compare

Ionic aur covalent compounds ek nazar mein

Ionic compounds

Crystal lattice mein cations aur anions se bane
Aam taur par paani mein ghulte hain, kerosene mein nahi
Ghulne ya pighalne par conduct karte hain, solid roop mein nahi
High melting points (sodium chloride: 801 °C)

Covalent compounds

Alag-alag molecules se bane
Aksar kerosene mein ghulte hain; kuch, jaise cheeni, paani mein ghulte hain
Aam taur par conduct nahi karte, ghulne ya pighalne par bhi nahi
Low melting points (naphthalene: lagbhag 80 °C)

Practice · 2 questions

Ruko aur socho: answers ke saath

Short answerMediumPause and Ponder Q19
Ek student ki notebook mein likha hai: 'Compound Z, safed crystals. Sookhe crystals: bulb band. Pighla hua: bulb jalta hai. Paani mein ghula: bulb jalta hai.' Z mein kis tarah ki bonding hai? Samjhao.
Solution dikhao
AnswerIonic bonding.
Z pighalne ya ghulne par conduct karta hai lekin solid roop mein nahi. Yeh ionic compound ka pattern hai: uske ions crystal mein bandh hote hain, lekin crystal pighalne ya ghulne par ghoomne ke liye free ho jaate hain aur current le jaate hain. Covalent compound teenon mein se kisi bhi state mein conduct nahi karta.
20
Short answerHardPause and Ponder Q20
Aluminium ke bartanon par ek dhundhli safed parat ban jaati hai, kyunki metal hawa ki oxygen ke saath react karta hai. Aluminium ka atomic number 13 hai.
1. Aluminium aur oxygen kaun se ions banate hain?
  Solution dikhao
  Answer $A l^{3 +}$ aur $O^{2 -}$
  Aluminium 2, 8, 3 hai, isliye woh teen electrons kho kar $A l^{3 +}$ banata hai. Oxygen 2, 6 hai, isliye woh do le kar $O^{2 -}$ banata hai.
2. Parat ka formula kya hai?
  Solution dikhao
  Answer $A l_{2} O_{3}$
  Charge numbers 3 aur 2 ko cross karne se $A l_{2} O_{3}$ milta hai: $2 \times (+ 3) + 3 \times (- 2) = 0$ .
3. Pighalne ke baad kya yeh oxide electricity conduct karega?
  Haan, kyunki uske ions ghoomne ke liye free hainNahi, kyunki usmein ions nahi hain
  Answer dekho
  Answer (A) Haan, kyunki uske ions ghoomne ke liye free hain
  Aluminium oxide ionic hai, aur pighalne se uske ions free ho jaate hain. Asal mein, aluminium metal ko pighle hue mineral mein ghule aluminium oxide se electricity guzaar kar nikaala jaata hai.

9.7 Covalent Compounds ka Molecular Mass

Atoms itne halke hain ki unhe ek-ek karke grams mein tola nahi ja sakta, isliye chemists unhe apne hi ek scale par compare karte hain. Atomic mass unit, u, carbon-12 atom ke mass ka barahvaan hissa hai, jo lagbhag ek proton ya ek neutron ke mass ke barabar hai. Is scale par hydrogen atom ka mass lagbhag 1 u aur oxygen atom ka 16 u hai. Table school chemistry mein use hone wali rounded values deti hai; chlorine ka 35.5 u ek average hai, kyunki natural chlorine do isotopes ka mixture hai.

Table 9.10Round kiye gaye atomic masses

Atom	Mass (u)	Atom	Mass (u)	Atom	Mass (u)
H	1	Na	23	K	39
C	12	Mg	24	Ca	40
N	14	Al	27	Fe	56
O	16	P	31	Cu	63.5
F	19	S	32	Zn	65
Li	7	Cl	35.5	Ba	137

Molecular mass nikaalna bas hisaab-kitaab hai: formula mein har tarah ke atom gino, use uske atomic mass se multiply karo, aur results jod do.

Definition

Molecular mass

Ek molecule ka u mein mass, jo usmein maujood har atom ke atomic masses jod kar milta hai.

ExampleWater, $H_{2} O$ : $2 \times 1 + 16 = 18$ u.

3/3Ek $C a^{2 +}$ aur do $C l^{-}$ : $C a C l_{2}$ ka formula unit mass = 111 u.

Fig. 9.12Molecular mass aur formula unit mass, dono atomic masses ke jod hain.NCERT 9.7–9.8 · p. 179

Left mein ammonia molecule ek bade N ball ke roop mein bana hai jisse teen chhote H balls jude hain; tags par nitrogen ke liye 14 u aur har hydrogen ke liye 1 u likha hai. Doosre step mein neeche sum 14 + 1 + 1 + 1 = 17 u dikhta hai. Teesre step mein, right par, a formula unit heading wale ek dashed box mein ek calcium ion aur do chloride ions hain, jin par 40 u aur 35.5 u har ek likha hai, aur neeche sum 40 + 35.5 + 35.5 = 111 u hai.

Example 9.4NCERT Example 9.4 · p. 179

Ammonia ka molecular mass

Ammonia, $N H_{3}$ , ka molecular mass nikaalo. (N = 14 u, H = 1 u)

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Example 9.5NCERT Example 9.5 · p. 179

Glucose ka molecular mass

Glucose, jo ORS mein aur tumhare khoon mein maujood sugar hai, ka formula $C_{6} H_{12} O_{6}$ hai. Iska molecular mass nikaalo. (C = 12 u, H = 1 u, O = 16 u)

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Yahi sum table salt ke liye try karo, to shabdon ki ek problem aati hai. Namak ka daana ions ki ek badi lattice hai (salt crystal), jismein alag NaCl molecules hote hi nahi, isliye sahi maayne mein uska koi molecular mass nahi hota. Section 9.8 woh shabd batata hai jo chemists iski jagah use karte hain.

Quick check

3 mein se 1

Sulfuric acid,

H_{2} S O_{4}

, ka molecular mass nikaalo. (H = 1 u, S = 32 u, O = 16 u)

Answer dekho

Answer 98 u

2 \times 1 + 32 + 4 \times 16 = 2 + 32 + 64 = 98

9.8 Ionic Compounds ka Formula Unit Mass

Ionic compound ka formula uske ions ka sabse simple whole-number ratio deta hai. Us ratio mein ions ke ek group ko, jaise calcium chloride mein ek $C a^{2 +}$ ion ke saath do $C l^{-}$ ions, formula unit kehte hain. Ek formula unit ke atomic masses jodo to formula unit mass (सूत्र इकाई द्रव्यमान) milta hai. Hisaab molecular mass jaisa hi hai. Sirf naam badalta hai, yeh yaad dilane ke liye ki formula unit ions ginne ka ek tarika hai, akele exist karne wala particle nahi. Electron lene ya khone se atom ka mass itna kam badalta hai ki yahan uska koi farak nahi padta.

Definition

Formula unit mass

Ionic compound ke ek formula unit (uske ions ka sabse simple whole-number group) ka u mein mass, jo usmein har atom ke atomic masses jod kar milta hai.

ExampleSodium chloride, NaCl: $23 + 35.5 = 58.5$ u.

Example 9.6NCERT Example 9.6 · p. 179

Calcium chloride ka formula unit mass

Thande deshon mein barf pighlane ke liye sadkon par calcium chloride, $C a C l_{2}$ , chhidka jaata hai. Iska formula unit mass nikaalo. (Ca = 40 u, Cl = 35.5 u)

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Example 9.7NCERT Example 9.7 · p. 180

Brackets ke saath formula unit mass

Calcium phosphate, $C a_{3} (P O_{4})_{2}$ , calcium supplement ke roop mein bikta hai aur kuch food powders mein daala jaata hai taaki unmein gaanthein na banein. Iska formula unit mass nikaalo. (Ca = 40 u, P = 31 u, O = 16 u)

Pehle khud try karo. Phir solution ek-ek step karke kholo.

InteractiveFormula builder

Ek interactive formula builder. Do menus mein se ek mein chaudah cations (sodium se ferric tak) aur doosre mein terah anions (chloride se phosphate tak) mein se chuna jaata hai, har ek apne charge ke saath. Ek panel dono ions ko unke charges aur ek crossing sign ke saath dikhata hai. Numbered steps criss-cross samjhate hain: charge numbers jagah badalte hain, common factor ho to divide ho jaata hai, polyatomic ion ek se zyada baar aaye to brackets lagte hain, aur ek check dikhata hai ki positive aur negative charges jud kar zero ho jaate hain. Result box formula, compound ka naam aur rounded atomic masses se nikaala formula unit mass dikhata hai. Ek checkbox Show button dabane tak answer chhupa kar rakhta hai, taaki learners pehle predict kar sakein, aur buttons random pair chunte ya reset karte hain.

Fig. 9.13Ek cation aur ek anion chuno. Builder charges ko cross karta hai, simplify karta hai, brackets lagata hai aur formula unit mass nikaalta hai.

Quick check

3 mein se 1

Magnesium chloride,

M g C l_{2}

, ka formula unit mass nikaalo. (Mg = 24 u, Cl = 35.5 u)

Answer dekho

Answer 95 u

24 + 2 \times 35.5 = 24 + 71 = 95

Recap

Summary aur key points

Chemical reaction mein products ka weight bilkul reactants jitna hota hai; mass sirf tab badalta hua lagta hai jab koi gas nikal jaaye ya andar aaye (Section 9.1).
Pure compound ki mass ke hisaab se ek fixed recipe hoti hai, isliye kahin ke bhi samples match karte hain: carbon dioxide mein carbon aur oxygen hamesha 3 : 8 hote hain, aur paani mein hydrogen aur oxygen 1 : 8 (Section 9.2).
Dalton ne dono laws explain kiye: reactions mein atoms na bante hain na nasht hote hain, woh bas regroup hote hain, aur fixed whole-number ratios mein judte hain (Section 9.3).
Atoms judkar $O_{2}$ aur $C O_{2}$ jaise molecules banate hain, jo akele exist kar sakte hain; noble gases akele atoms ke roop mein rehti hain (Section 9.4).
Atoms full outer shell tak pahunchne aur apni energy kam karne ke liye bond banate hain, electrons share karke ya transfer karke; isse bana attraction chemical bond hai (Section 9.4).
Covalent bond electrons ka ek shared pair hai: H–H aur Cl–Cl mein ek pair, O=O mein do, N≡N mein teen (Section 9.4.1).
Do elements wale covalent compounds ke naam number prefixes se rakhe jaate hain: $S O_{3}$ sulfur trioxide hai aur $N_{2} O$ dinitrogen monoxide (Covalent compounds ke naam rakhna).
Ionic bond cation (electrons khone wala atom) aur anion (electrons lene wala atom) ke beech ka attraction hai; ionic solids 3-D crystal lattices hote hain (Section 9.4.2).
Ionic compounds ke naam mein pehle cation aata hai; $S O_{4}^{2 -}$ aur $N H_{4}^{+}$ jaise polyatomic ions ek unit ki tarah kaam karte hain (Ionic compounds ke naam rakhna).
Formula likhne ke liye valencies ya charges ko cross karo, simplify karo, aur ek se zyada baar aane wale polyatomic ion par bracket lagao; charges ka jod zero hona chahiye (Section 9.5).
Ionic compounds aam taur par paani mein ghulte hain, ghulne ya pighalne par conduct karte hain, aur high temperatures par pighalte hain; covalent compounds aam taur par conduct nahi karte (Section 9.6).
Molecular mass (molecules ke liye) aur formula unit mass (ionic compounds ke liye) atomic masses ke jod hain: $H_{2} S O_{4}$ 98 u hai aur $C a C l_{2}$ 111 u (Section 9.7, Section 9.8).

Practice · 18 questions

Practice questions answers ke saath (NCERT “Dohraao, socho, sudhaaro”)

1
Short answerMediumNCERT Exercises Q1
Ek student ke flash card par likha hai: 'Element P: atomic number 12. Element Q: atomic number 9.'
1. Har ek ka electron arrangement likho, aur batao ki har ek kaunsa ion banata hai.
  Solution dikhao
  AnswerP 2, 8, 2 hai aur $P^{2 +}$ banata hai; Q 2, 7 hai aur $Q^{-}$ banata hai.
  P (12 electrons) 2, 8, 2 hai. Apne do outer electrons khone se full shell bachta hai, isliye woh 2+ charge wala cation banata hai. Q (9 electrons) 2, 7 hai; ek electron lene se uska octet poora hota hai, isliye woh 1− charge wala anion banata hai.
2. P aur Q milne par kis type ka bond banta hai?
  IonicCovalent
  Answer dekho
  Answer (A) Ionic
  P electrons Q ko transfer karta hai, isliye opposite charge wale ions bante hain aur attract karte hain: yeh ionic bond hai.
3. Compound ka formula likho.
  Solution dikhao
  Answer $P Q_{2}$
  Charges 2+ aur 1− cross hokar $P_{1} Q_{2}$ dete hain, jise $P Q_{2}$ likhte hain. (P magnesium hai aur Q fluorine, isliye compound $M g F_{2}$ hai.)
2
DiagramHardNCERT Exercises Q2
Hawa ka zyadatar hissa banane wali ek colourless gas diatomic molecules se bani hai. Uske atoms ka atomic number 7 hai.
1. Atom ka electron arrangement likho aur samjhao ki do atoms kyun judte hain.
  Solution dikhao
  Answer2, 5: har atom mein octet ke liye teen kam hain; sharing se dono poore ho jaate hain.
  Saat electrons shells ko 2, 5 ki tarah bharte hain. Akele, har atom mein octet ke liye teen electrons kam hain. Agar do atoms teen pairs share karein, to dono aath electrons gin sakte hain, isliye woh $N_{2}$ ke roop mein judte hain.
2. Molecule ko kis tarah ka bond jode rakhta hai?
  Single covalent bondDouble covalent bondTriple covalent bondIonic bond
  Answer dekho
  Answer (C) Triple covalent bond
  Teen shared pairs se triple bond banta hai, N≡N.
3. Yahi element hydrogen ke saath judta hai. Compound ka formula do aur uske bonds describe karo.
  Solution dikhao
  Answer $N H_{3}$ : teen single N–H bonds aur N par ek unshared pair.
  Nitrogen ko teen electrons chahiye aur har hydrogen atom ek share kar sakta hai, isliye teen hydrogen atoms ek nitrogen atom se judte hain, har ek single covalent bond se. Nitrogen ke paas ek unshared pair bachta hai, isliye uske 8 electrons gine jaate hain; har hydrogen ke 2. Compound ammonia, $N H_{3}$ , hai.
Quick answerMediumNCERT Exercises Q3
Ek ionic compound ke formula unit mein teen cations aur do anions hain, aur uske charges balance hote hain. Yeh ions ke kis pair se bana ho sakta hai?
$A l^{3 +}$ aur $O^{2 -}$ $N a^{+}$ aur $S O_{4}^{2 -}$ $M g^{2 +}$ aur $C l^{-}$ $C a^{2 +}$ aur $P O_{4}^{3 -}$
Answer dekho
Answer (D) $C a^{2 +}$ aur $P O_{4}^{3 -}$
Teen $C a^{2 +}$ se +6 aur do $P O_{4}^{3 -}$ se −6 milta hai: $C a_{3} (P O_{4})_{2}$ . Aluminium oxide mein do cations aur teen anions hain, sodium sulfate mein do aur ek, aur magnesium chloride mein ek aur do.
4
Quick answerMediumNCERT Exercises Q4
Inmein se kaun se statements sahi hain? Jitne sahi hon, sab chuno.
Ozone, $O_{3}$ , ke molecule mein teen oxygen atoms hote hain.Har element do ya zyada atoms ke molecules ke roop mein exist karta hai.Ammonia ke molecule mein chaar atoms hote hain.Carbon dioxide mein carbon har oxygen atom se single bond se juda hai.
Saare sahi options chuno
Answer dekho
Answer
(A) Ozone, $O_{3}$ , ke molecule mein teen oxygen atoms hote hain.
(C) Ammonia ke molecule mein chaar atoms hote hain.
A sahi hai (teen O atoms) aur C sahi hai (ek N aur teen H). B galat hai: helium aur argon jaisi noble gases akele atoms ke roop mein rehti hain. D galat hai: carbon har oxygen atom ke saath do pairs share karta hai, isliye dono bonds double bonds hain, O=C=O.
5
Short answerMediumNCERT Exercises Q5
Har compound ka chemical formula likho.
1. zinc nitrate
  Solution dikhao
  Answer $Z n (N O_{3})_{2}$
  $Z n^{2 +}$ aur $N O_{3}^{-}$ : ek zinc ko do nitrates chahiye, brackets mein: $Z n (N O_{3})_{2}$ .
2. barium oxide
  Solution dikhao
  Answer $B a O$
  $B a^{2 +}$ aur $O^{2 -}$ cross hokar $B a_{2} O_{2}$ dete hain, jo simplify hokar $B a O$ banta hai.
3. ferric sulfate
  Solution dikhao
  Answer $F e_{2} (S O_{4})_{3}$
  Ferric $F e^{3 +}$ hai aur sulfate $S O_{4}^{2 -}$ . Cross karne se do iron ions aur teen sulfate ions milte hain: $F e_{2} (S O_{4})_{3}$ . Check: $2 \times 3 = 6$ aur $3 \times 2 = 6$ .
4. cupric hydroxide
  Solution dikhao
  Answer $C u (O H)_{2}$
  Cupric $C u^{2 +}$ hai aur hydroxide $O H^{-}$ , isliye brackets mein do hydroxide ions: $C u (O H)_{2}$ .
6
Short answerMediumNCERT Exercises Q6
Ions ke har pair se bane compound ka formula likho.
1. $B a^{2 +}$ aur $F^{-}$
  Solution dikhao
  Answer $B a F_{2}$
  Charges 2 aur 1 cross hokar $B a_{1} F_{2}$ dete hain: $B a F_{2}$ .
2. $N H_{4}^{+}$ aur $S O_{4}^{2 -}$
  Solution dikhao
  Answer $(N H_{4})_{2} S O_{4}$
  Do ammonium ions ek sulfate ion ko balance karte hain. Ammonium do baar aata hai, isliye uspar bracket hai: $(N H_{4})_{2} S O_{4}$ .
3. $L i^{+}$ aur $C O_{3}^{2 -}$
  Solution dikhao
  Answer $L i_{2} C O_{3}$
  Do lithium ions ek carbonate ion ko balance karte hain. Carbonate ek baar aata hai, isliye brackets nahi: $L i_{2} C O_{3}$ .
4. $F e^{3 +}$ aur $N O_{3}^{-}$
  Solution dikhao
  Answer $F e (N O_{3})_{3}$
  Teen nitrate ions ek ferric ion ko balance karte hain: $F e (N O_{3})_{3}$ .
Quick answerEasyNCERT Exercises Q7
Magnesium ka atomic number 12 hai. Magnesium ion, $M g^{2 +}$ , ka electron arrangement kaunsa hai?
2, 8, 22, 82, 8, 42, 8, 8
Answer dekho
Answer (B) 2, 8
$M g^{2 +}$ mein $12 - 2 = 10$ electrons hain, jo 2, 8 arranged hain. Arrangement 2, 8, 2 neutral atom ka hai, aur 2, 8, 4 ka matlab hota ki usne electrons liye hain.
8
NumericalMediumNCERT Exercises Q8
Har substance ka molecular mass ya formula unit mass nikaalo. (H = 1, C = 12, N = 14, O = 16, S = 32, K = 39, Ca = 40, sab u mein)
1. ammonium sulfate, $(N H_{4})_{2} S O_{4}$ , ek fertiliser
  u
  Answer dekho
  Answer 132 u
  $2 \times (14 + 4) + 32 + 4 \times 16 = 36 + 32 + 64 = 132$ u.
2. urea, $C O (N H_{2})_{2}$ , sabse zyada use hone wala nitrogen fertiliser (ek covalent compound)
  u
  Answer dekho
  Answer 60 u
  Molecular mass $= 12 + 16 + 2 \times (14 + 2) = 28 + 32 = 60$ u.
3. potassium nitrate, $K N O_{3}$ , jo fertilisers aur pataakhon mein use hota hai
  u
  Answer dekho
  Answer 101 u
  $39 + 14 + 3 \times 16 = 101$ u.
4. calcium carbonate, $C a C O_{3}$ , jisse chalk aur marble bante hain
  u
  Answer dekho
  Answer 100 u
  $40 + 12 + 3 \times 16 = 100$ u.
9
Short answerMediumNCERT Exercises Q9
Jab elements ka har pair react karta hai, to bane compound ka formula likho.
1. potassium aur oxygen
  Solution dikhao
  Answer $K_{2} O$
  $K^{+}$ aur $O^{2 -}$ cross hokar $K_{2} O$ dete hain.
2. aluminium aur sulfur
  Solution dikhao
  Answer $A l_{2} S_{3}$
  $A l^{3 +}$ aur $S^{2 -}$ cross hokar $A l_{2} S_{3}$ dete hain.
3. barium aur nitrogen
  Solution dikhao
  Answer $B a_{3} N_{2}$
  Barium $B a^{2 +}$ banata hai aur nitrogen (2, 5) teen electrons le kar nitride ion $N^{3 -}$ banata hai. Cross karne se $B a_{3} N_{2}$ milta hai.
4. lithium aur fluorine
  Solution dikhao
  Answer $L i F$
  $L i^{+}$ aur $F^{-}$ 1 : 1 mein judte hain: $L i F$ .
Short answerMediumNCERT Exercises Q10
Grid ko copy karke poora karo, har cation (left) aur anion (upar) se bane compound ke formula se. Ek cell tumhare liye bhar diya gaya hai.
Table 9.11
$O H^{-}$ $O^{2 -}$ $P O_{4}^{3 -}$
$K^{+}$ $K O H$ ? ?
$C a^{2 +}$ ? ? ?
$A l^{3 +}$ ? ? ?
Solution dikhao
Table 9.12
$O H^{-}$ $O^{2 -}$ $P O_{4}^{3 -}$
$K^{+}$ $K O H$ $K_{2} O$ $K_{3} P O_{4}$
$C a^{2 +}$ $C a (O H)_{2}$ $C a O$ $C a_{3} (P O_{4})_{2}$
$A l^{3 +}$ $A l (O H)_{3}$ $A l_{2} O_{3}$ $A l P O_{4}$
Barabar charges ek-ke-badle-ek cancel ho jaate hain ( $C a O$ , $A l P O_{4}$ ). Brackets sirf wahan aate hain jahan polyatomic ion ek se zyada baar aata hai, jaise $C a (O H)_{2}$ aur $C a_{3} (P O_{4})_{2}$ mein.
11
NumericalMediumNCERT Exercises Q11
Zinc ke daane dilute sulfuric acid ke saath react karte hain. Band flask mein 6.5 g zinc aur 9.8 g sulfuric acid se 16.1 g zinc sulfate aur 0.2 g hydrogen gas milti hai.
1. Dikhao ki yeh masses law of conservation of mass ko follow karte hain.
  Solution dikhao
  AnswerReactants 16.3 g = products 16.3 g.
  Reactants: $6.5 + 9.8 = 16.3$ g. Products: $16.1 + 0.2 = 16.3$ g. Totals barabar hain, isliye law sahi hai.
2. Yahi reaction balance par rakhe khule beaker mein kiya jaata hai, aur saari hydrogen nikal jaati hai. Aakhir mein balance andar ki cheezon ka kitna mass dikhata hai?
  g
  Answer dekho
  Answer 16.1 g
  Sirf gas nikalti hai: $16.3 - 0.2 = 16.1$ g. Law ab bhi sahi hai; balance bas ab hydrogen ko nahi tol raha.
12
Short answerMediumNCERT Exercises Q12
Ek particle mein 16 protons, 16 neutrons aur 18 electrons hain.
1. Iska atomic number aur mass number kya hai?
  Solution dikhao
  AnswerAtomic number 16 aur mass number 32.
  Atomic number = protons ki sankhya = 16. Mass number = protons + neutrons = $16 + 16 = 32$ .
2. Kya is par koi charge hai? Agar hai, to yeh cation hai ya anion, aur kyun?
  Solution dikhao
  Answer2− charge wala anion.
  Ismein protons (16) se do zyada electrons (18) hain, isliye iska charge $16 - 18 = - 2$ hai: yeh anion hai.
3. Iska electron arrangement likho.
  Solution dikhao
  Answer2, 8, 8
  18 electrons shells ko 2, 8, 8 ki tarah bharte hain.
4. Particle ka naam batao.
  Solution dikhao
  AnswerSulfide ion, $S^{2 -}$ .
  Atomic number 16 sulfur hai, aur do electrons lene wala sulfur atom sulfide ion, $S^{2 -}$ , hai.
13
Short answerHardNCERT Exercises Q13
Do non-metals, A aur B, ke atoms hain: A mein 6 aur B mein 8 electrons hain.
1. Har ek ka electron arrangement likho aur batao ki octet poora karne ke liye har atom ko kitne electrons chahiye.
  Solution dikhao
  AnswerA 2, 4 hai aur use 4 chahiye; B 2, 6 hai aur use 2 chahiye.
  A (6 electrons) 2, 4 hai, isliye use 4 aur chahiye. B (8 electrons) 2, 6 hai, isliye use 2 aur chahiye.
2. A aur B ionic compound banayenge ya covalent? Samjhao.
  Solution dikhao
  AnswerCovalent: woh electrons share karte hain.
  Dono non-metals hain. A ko chaar electrons khone ya lene padte, jismein bahut zyada energy lagti hai, aur B apne electrons ko itni mazbooti se pakadta hai ki koi de nahi sakta. Isliye koi bhi atom electrons nahi deta; balki woh pairs share karte hain, jisse covalent bonds bante hain.
3. Compound ka formula likho aur uska naam batao.
  Solution dikhao
  Answer $A B_{2}$ , jo $C O_{2}$ , carbon dioxide, hai.
  Valencies 4 aur 2 cross hokar $A_{2} B_{4}$ dete hain, jo simplify hokar $A B_{2}$ banta hai. A carbon hai aur B oxygen, isliye compound carbon dioxide, $C O_{2}$ , hai, jismein do double bonds hain, O=C=O.
Quick answerMediumNCERT Exercises Q14
Assertion (A): Naphthalene kerosene mein ghulta hai lekin paani mein nahi. Reason (R): Naphthalene ek ionic compound hai.
A aur R dono sahi hain, aur R, A ko explain karta haiA aur R dono sahi hain, lekin R, A ko explain nahi kartaA sahi hai, lekin R galat haiA galat hai, lekin R sahi hai
Answer dekho
Answer (C) A sahi hai, lekin R galat hai
A sahi hai. R galat hai: naphthalene molecules se bana covalent compound hai, aur isiliye woh kerosene mein ghulta hai, paani mein nahi, conduct nahi karta, aur sirf lagbhag 80 °C par pighal jaata hai.
15
Short answerMediumNCERT Exercises Q15
Har particle mein electrons aur neutrons ki sankhya nikaalo.
1. $_{}^{}_{}^{24} M g^{2 +}$ (atomic number 12)
  Solution dikhao
  Answer10 electrons, 12 neutrons
  Electrons: $12 - 2 = 10$ . Neutrons: $24 - 12 = 12$ .
2. $_{}^{}_{}^{19} F^{-}$ (atomic number 9)
  Solution dikhao
  Answer10 electrons, 10 neutrons
  Electrons: $9 + 1 = 10$ . Neutrons: $19 - 9 = 10$ .
3. $_{}^{}_{}^{56} F e^{3 +}$ (atomic number 26)
  Solution dikhao
  Answer23 electrons, 30 neutrons
  Electrons: $26 - 3 = 23$ . Neutrons: $56 - 26 = 30$ .
16
Quick answerEasy
Ionic compound ka formula likhne ke steps ko sahi order mein lagao.
1. Common factor se divide karo
2. Numbers ko cross karo
3. Neeche charges likho
4. Check karo ki charges cancel hote hain
5. Pehle cation, phir anion likho
Answer dekho
Answer
Pehle cation, phir anion likho
Neeche charges likho
Numbers ko cross karo
Common factor se divide karo
Check karo ki charges cancel hote hain
Pehle symbols, phir charges, cross, simplify, aur aakhir mein check karo ki total charge zero hai.
17
Quick answerEasy
Har substance ko un particles se match karo jinse woh bana hai.
Left mein koi item tap karo, phir right mein uska match.
Answer dekho
Answer
sodium chloride : lattice mein ions
argon : akele atoms
oxygen gas : element ke molecules
paani : compound ke molecules
Namak ionic hai, argon noble gas hai, oxygen $O_{2}$ molecules ke roop mein rehti hai aur paani $H_{2} O$ molecules ke roop mein.
Quick answerMedium
Ek particle mein 13 protons aur 10 electrons hain. Iska charge hai.
Answer dekho
Answer 3+
Electrons se $13 - 10 = 3$ protons zyada, isliye charge 3+ hai. Yeh aluminium ion, $A l^{3 +}$ , hai.

	$O H^{-}$	$O^{2 -}$	$P O_{4}^{3 -}$
$K^{+}$	$K O H$	?	?
$C a^{2 +}$	?	?	?
$A l^{3 +}$	?	?	?

	$O H^{-}$	$O^{2 -}$	$P O_{4}^{3 -}$
$K^{+}$	$K O H$	$K_{2} O$	$K_{3} P O_{4}$
$C a^{2 +}$	$C a (O H)_{2}$	$C a O$	$C a_{3} (P O_{4})_{2}$
$A l^{3 +}$	$A l (O H)_{3}$	$A l_{2} O_{3}$	$A l P O_{4}$

Apna NCERT exercise question dhoondo

Hamare practice questions ncert.ai ke liye likhe gaye hain aur NCERT exercises ko follow karte hain. Apni textbook ke question se match karne wala question dhoondo; uska answer uske saath hai.

Tumhari NCERT textbook mein	Yahan practice question
Pause and Ponder Q1	Ruko aur socho · Q1
Pause and Ponder Q2	Ruko aur socho · Q2
Pause and Ponder Q3	Ruko aur socho · Q3
Pause and Ponder Q4	Ruko aur socho · Q4
Pause and Ponder Q5	Ruko aur socho · Q5
Pause and Ponder Q6	Ruko aur socho · Q6
Pause and Ponder Q8	Ruko aur socho · Q8
Pause and Ponder Q9	Ruko aur socho · Q9
Pause and Ponder Q10	Ruko aur socho · Q10
Pause and Ponder Q11	Ruko aur socho · Q11
Pause and Ponder Q12	Ruko aur socho · Q12
Pause and Ponder Q13	Ruko aur socho · Q13
Pause and Ponder Q14	Ruko aur socho · Q14
Pause and Ponder Q15	Ruko aur socho · Q15
Pause and Ponder Q16	Ruko aur socho · Q16
Pause and Ponder Q17	Ruko aur socho · Q17
Pause and Ponder Q18	Ruko aur socho · Q18
Pause and Ponder Q19	Ruko aur socho · Q19
Pause and Ponder Q20	Ruko aur socho · Q20
NCERT Exercises Q1	Dohraao, socho, sudhaaro · Q1
NCERT Exercises Q2	Dohraao, socho, sudhaaro · Q2
NCERT Exercises Q3	Dohraao, socho, sudhaaro · Q3
NCERT Exercises Q4	Dohraao, socho, sudhaaro · Q4
NCERT Exercises Q5	Dohraao, socho, sudhaaro · Q5
NCERT Exercises Q6	Dohraao, socho, sudhaaro · Q6
NCERT Exercises Q7	Dohraao, socho, sudhaaro · Q7
NCERT Exercises Q8	Dohraao, socho, sudhaaro · Q8
NCERT Exercises Q9	Dohraao, socho, sudhaaro · Q9
NCERT Exercises Q10	Dohraao, socho, sudhaaro · Q10
NCERT Exercises Q11	Dohraao, socho, sudhaaro · Q11
NCERT Exercises Q12	Dohraao, socho, sudhaaro · Q12
NCERT Exercises Q13	Dohraao, socho, sudhaaro · Q13
NCERT Exercises Q14	Dohraao, socho, sudhaaro · Q14
NCERT Exercises Q15	Dohraao, socho, sudhaaro · Q15

Quick check: MCQs

Kya matter badalne par mass badalta hai?2 questions
9.1 Law of Conservation of Mass3 questions
9.2 Law of Constant Proportions3 questions
9.3 Dalton ki Atomic Theory3 questions
Covalent compounds ke naam rakhna3 questions
Ionic compounds ke naam rakhna4 questions
9.5.2 Ionic compounds ke chemical formulae likhna3 questions
9.6 Ionic aur Covalent Compounds ki Properties3 questions
9.7 Covalent Compounds ka Molecular Mass3 questions
9.8 Ionic Compounds ka Formula Unit Mass3 questions

Glossary · 15

Key terms (English + Hindi)

anionऋणायनrinayan: Negative charge wala ion, jo atom ke electrons lene se banta hai, jaise $C l^{-}$ .Chapter mein pehli baar yahan aaya →

cationधनायनdhanayan: Positive charge wala ion, jo atom ke electrons khone se banta hai, jaise $N a^{+}$ .Chapter mein pehli baar yahan aaya →
chemical bondरासायनिक आबंधrasayanik aabandh: Attraction ka woh force jo atoms ya ions ko jode rakhta hai.Chapter mein pehli baar yahan aaya →
chemical formulaरासायनिक सूत्रrasayanik sutra: Symbols aur subscripts jo substance ke elements aur unke proportions dikhate hain, jaise $H_{2} O$ .Chapter mein pehli baar yahan aaya →
covalent bondसहसंयोजी आबंधsahsanyoji aabandh: Woh bond jo do atoms ke electrons ka ek pair share karne se banta hai.

formula unit massसूत्र इकाई द्रव्यमानsutra ikai dravyaman: Ionic compound ke ek formula unit (sabse simple ion ratio) ka u mein mass, jo atomic masses jod kar milta hai.Chapter mein pehli baar yahan aaya →

ionआयनaayan: Atom ya atoms ka group jis par electric charge hota hai, kyunki usne electrons khoye ya liye hain.Chapter mein pehli baar yahan aaya →
ionic bondआयनिक आबंधaayanik aabandh: Opposite charge wale ions ke beech ka electrostatic attraction.Chapter mein pehli baar yahan aaya →

law of conservation of massद्रव्यमान संरक्षण का नियमdravyaman sanrakshan ka niyam: Chemical reaction mein products ka total mass reactants ke total mass ke barabar hota hai; matter na banta hai na nasht hota hai.Chapter mein pehli baar yahan aaya →
law of constant proportionsस्थिर अनुपात का नियमsthir anupat ka niyam: Compound ke har pure sample mein elements mass ke hisaab se same ratio mein hote hain, chahe sample kahin se bhi aaye.Chapter mein pehli baar yahan aaya →

molecular massआण्विक द्रव्यमानaanvik dravyaman: Ek molecule ka u mein mass, jo usmein har atom ke atomic masses jod kar milta hai.
moleculeअणुanu: Substance ka sabse chhota particle jo akela exist kar sake: do ya zyada jude atoms, bina overall charge ke.

polyatomic ionबहुपरमाणुक आयनbahuparmanuk aayan: Bonded atoms ka charged group jo ek unit ki tarah kaam karta hai, jaise $S O_{4}^{2 -}$ ya $N H_{4}^{+}$ .Chapter mein pehli baar yahan aaya →
postulateअभिधारणाabhidharana: Theory ka starting point maana gaya basic idea; use usse nikalne wali predictions se test kiya jaata hai.Chapter mein pehli baar yahan aaya →

valencyसंयोजकताsanyojakta: Atom ya ion ki combining capacity: jitne electrons woh share karta hai, ya uske charge ka size.Chapter mein pehli baar yahan aaya →

Kya matter badalne par mass badalta hai?

9.1 Law of Conservation of Mass

9.2 Law of Constant Proportions

9.3 Dalton ki Atomic Theory

9.4 Atoms Kaise Judte Hain

9.4.1 Electrons share karke bonding: covalent bond

Elements ke molecules

Compounds ke molecules

Covalent compounds ke naam rakhna

9.4.2 Electron transfer se bonding: ionic bond

Ionic compounds ke naam rakhna

9.5 Chemical Formulae Likhna

9.5.1 Covalent compounds ke chemical formulae likhna

9.5.2 Ionic compounds ke chemical formulae likhna

9.6 Ionic aur Covalent Compounds ki Properties

9.7 Covalent Compounds ka Molecular Mass

9.8 Ionic Compounds ka Formula Unit Mass

Apna NCERT exercise question dhoondo

Quick check: MCQs

Tum chapter ke end tak pahunch gaye