NCERT Exercise Solutions
Chapter 8 ke saare 12 sawaal, aasaan Hinglish mein, poore kaaran ke saath. Exam se pehle ka final revision! 📘✅
🧭 Is Post Mein
📖 Kahani: Homework Table ka Jhagda
Sunday ki dopahar. Golu, Rohan aur Priya ek hi table par chapter 8 ke exercise solve karne baithe. Table par paani ka glass, namak ki katori aur kuch kankad pade the.
Golu ne paani ki taraf ishaara kiya: “Paani mein hydrogen aur oxygen hain, toh paani mixture hua na?”
Rohan bola: “Nahi yaar! Hydrogen jalti hai, oxygen jalne mein madad karti hai, aur paani toh aag bujhata hai. Mixture hota toh dono ke gun dikhte.”
Priya ne namak ki katori uthayi: “Aur yeh namak? Isme sodium aur chlorine hain. Ek-ek karke sochte hain: element, compound ya mixture?”
Teeno ko samajh aaya ki exercise ke saare sawaal ek hi chaabi se khulte hain. Aaj hum wahi chaabi seekhenge aur NCERT ke saare 12 sawaal step-by-step solve karenge. 🔑
🎯 Is Post Mein Kya Seekhenge
- Chapter 8 ke end ke saare 12 exercise sawaalon ke poore, kaaran wale jawaab
- Kisi bhi padarth ko element, compound ya mixture mein baantne ka 3-sawaal wala tareeka
- MCQ aur Assertion–Reason mein galat options kaise kaatein
- Word equation sahi tareeke se kaise likhein (loha + gandhak, loha + acid)
- “Justify karo” wale sawaalon mein poore marks ka formula
🧱 Basics: Pehle Yeh Aana Chahiye
1. Mixture: do ya zyada padarth bas mile hue, har ek apne gun rakhta hai, anupaat kuch bhi. (Post 1: Mixture Kya Hai?, Post 2: Mixtures ke Prakar)
2. Pure substance: jisme ek hi tarah ke kan hon aur banaavat har jagah same ho. (Post 3)
3. Element: jise chemical tareeke se aur saral padarth mein toda na ja sake. (Post 4: Elements)
4. Compound: do ya zyada elements fixed anupaat mein chemically jude, naye gun ke saath. (Post 5: Compounds, Post 6: Mixture vs Compound)
5. Use aur minerals: alloys, cement, minerals. (Post 7, Post 8: Minerals)
💡 Concept: Har Sawaal ki Chaabi (3 Sawaal ka Test)
Chapter 8 ka lagbhag har exercise sawaal ek hi baat poochhta hai: yeh padarth kis group mein hai, aur kyun? Iske liye bas yeh teen sawaal apne aap se poochho:
Nahi → Mixture. Haan → Pure substance, agle sawaal par jao.
Nahi → Element. Haan → Compound.
Haan → Uniform (jaise hawa, namak ka ghol, brass). Nahi → Non-uniform (jaise ret, keechad wala paani).
Jaise: “Paani ek compound hai, kyunki usme hydrogen aur oxygen fixed anupaat (2:1 atom) mein chemically jude hain aur bijli guzaarne par woh toot jaata hai.”
Sirf “compound” likhne par aadhe marks milte hain; “kyunki…” wala hissa poore marks dilaata hai.
📘 NCERT Exercise Solutions (Q1–Q12)
Har sawaal ko yahan chhote roop mein apne shabdon mein likha gaya hai. Poora sawaal NCERT book ke “Keep the curiosity alive” hisse mein dekho. Jawaab dekhne ke liye click karo, par pehle khud koshish zaroor karna! 💪
Q1 A + B se C banta hai. A aur B ko chemical reaction se aur saral padarthon mein toda nahi ja sakta. Chaar options mein se sahi kathan chuno.
✅ Option (iv): A aur B elements hain, aur C ek compound hai jiski banaavat fixed hai.
Kyun? Jo padarth chemical tareeke se aur saral na ho sake, wahi element hai. Toh A aur B elements hain. Do elements reaction karke naya padarth banayein, toh woh compound hai, aur compound ki banaavat hamesha fixed hoti hai.
Baaki options galat kyun: (i) aur (iii) A aur B ko compound bata rahe hain, jo sawaal ki shart ke ulat hai. (ii) C ko compound toh sahi kehta hai, par sawaal ki asli baat (A aur B toot nahi sakte, yaani element hain) nahi batata. Sabse poora aur sahi kathan (iv) hi hai.
Q2 Assertion: Hawa ek mixture hai. Reason: Jab padarth bina chemical badlav ke mil jaate hain, toh mixture banta hai. Sahi option chuno.
✅ Option (i): Assertion aur Reason dono sahi hain, aur Reason, Assertion ko sahi samjhata hai.
Kyun? Hawa mein nitrogen (lagbhag 78%), oxygen, argon, carbon dioxide aur paani ki bhaap bas mile hue hain. Inke beech koi chemical reaction nahi hota; har gas apne gun rakhti hai (oxygen saans aur jalne mein madad karti hai, carbon dioxide chuna-paani ko doodhiya karti hai). Yahi mixture ki paribhasha hai, isliye Reason seedha batata hai ki hawa mixture kyun hai.
Q3 Paani ek compound hai. Uske gun oxygen aur hydrogen se alag kyun hain? Kaaran do.
Compound banne mein elements ke beech chemical reaction hota hai. Isse ek bilkul naya padarth banta hai jiske gun naye hote hain.
| Gun | Hydrogen | Oxygen | Paani |
|---|---|---|---|
| Kamre ke taapmaan par avastha | Gas | Gas | Liquid (drav) |
| Aag ke saath | Khud jalti hai | Jalne mein madad karti hai | Aag bujhata hai |
Paani mein hydrogen aur oxygen fixed anupaat (har paani ke kan mein 2 hydrogen atom, 1 oxygen atom) mein chemically jude hain. Jab tak jude hain, tab tak unke apne gun “chhup” jaate hain. Isliye paani ke gun alag hain. Mixture mein aisa nahi hota.
Q4 Kis option mein saare udaaharan sahi group mein hain? (i) Elements: paani, nitrogen, loha, hawa (ii) Uniform mixtures: minerals, samudri paani, bronze, hawa (iii) Pure substances: carbon dioxide, loha, oxygen, cheeni (iv) Non-uniform mixtures: hawa, ret, brass, keechad wala paani
✅ Option (iii) sahi hai. Carbon dioxide aur cheeni compound hain, loha aur oxygen element hain. Element aur compound dono pure substance hain.
Baaki galat kyun:
- (i) Paani compound hai aur hawa mixture; dono element nahi.
- (ii) Minerals ki banaavat fixed hoti hai, woh mixture nahi (pure substance) hain. Baaki teen sahi hain, par ek galat hone se option galat.
- (iv) Hawa aur brass uniform mixtures hain, non-uniform nahi.
Q5 Loha nam hawa se reaction karke iron oxide banata hai; magnesium oxygen mein jal kar magnesium oxide banata hai. Har padarth ko element, compound ya mixture mein baanto, kaaran ke saath.
| Padarth | Group | Kaaran |
|---|---|---|
| Loha (iron) | Element | Sirf ek tarah ke atom; aur saral nahi kiya ja sakta |
| Nam hawa (moist air) | Mixture | Oxygen, nitrogen, paani ki bhaap aadi bina fixed anupaat ke mile hain |
| Iron oxide (zang) | Compound | Loha aur oxygen chemically jude; naye gun (laal-bhoora, bhurbhura, loha jaisi chamak aur mazbooti nahi) |
| Magnesium | Element | Ek hi tarah ke atom wala metal |
| Oxygen | Element | Ek hi tarah ke atom (O₂ molecule mein dono atom oxygen ke) |
| Magnesium oxide | Compound | Magnesium aur oxygen fixed anupaat mein jude; safed powder, magnesium jaisa chamakdaar nahi |
Q6 19 padarthon ko Elements, Compounds aur Mixtures ki table mein bharo, phir unme se pure substances bataao.
| Elements (6) | Compounds (8) | Mixtures (5) |
|---|---|---|
| Aluminium Gold (sona) Oxygen Nitrogen Sulfur Hydrogen | Carbon dioxide Magnesium oxide Rust (zang, iron oxide) Iron sulfide Glucose Paani Sodium chloride (namak) Baking soda | Ret (sand) Samudri paani Keechad wala paani Hawa Phalon ka juice |
Pure substances: saare elements aur saare compounds, yaani upar ki pehli do columns ke 14 padarth. Mixtures (5) pure substance nahi hain.
Check: 6 + 8 + 5 = 19, saare padarth aa gaye. Ret ko mixture isliye rakha kyunki usme quartz, mica aur doosre minerals ke alag-alag daane hote hain.
Q7 Loha choorn aur sulfur powder ka mixture garam karne par kya naya padarth banta hai? Woh mixture se kaise alag hai? Word equation likho.
Naya padarth: iron sulfide (ek kaala-bhoora thos).
Word equation: Loha (iron) + Sulfur —(garam karne par)→ Iron sulfide
| Jaanch | Mixture (loha + sulfur) | Iron sulfide (compound) |
|---|---|---|
| Magnet paas laao | Loha ke kan chipak jaate hain, peela sulfur reh jaata hai | Magnet ki taraf nahi khinchta |
| Alag karna | Magnet jaise bhautik tareeke se alag ho jaata hai | Bhautik tareeke se alag nahi hota |
| Dikhawat | Grey aur peele kan alag dikhte hain | Ek jaisa kaala-bhoora padarth |
| Dilute acid daalne par | Hydrogen gas (gandh nahi) | Hydrogen sulfide gas (sade ande jaisi gandh) |
| Anupaat | Kuch bhi | Fixed |
Q8 Kya koi padarth ek saath element aur compound dono ho sakta hai? Samjhao.
Nahi. Dono ki paribhasha ek-doosre ki ulti hai:
- Element ko chemical tareeke se aur saral nahi kiya ja sakta; usme ek hi tarah ke atom hote hain.
- Compound mein do ya zyada alag elements jude hote hain, aur use chemical tareeke se un elements mein toda ja sakta hai.
Jo cheez todi ja sakti hai woh element nahi, aur jo nahi todi ja sakti woh compound nahi. Isliye ek padarth dono nahi ho sakta.
Dhyaan do: O₂ ya H₂ jaise molecule mein do atom jude hain, par dono ek hi element ke hain. Isliye oxygen gas element hi hai, compound nahi.
Q9 Agar paani hydrogen aur oxygen ka compound na hokar unka mixture hota, toh roz ki zindagi kaise badalti?
- Paani gas hota: mixture mein dono gas apne gun rakhti, toh kamre ke taapmaan par “paani” liquid nahi, gas hota. Nadi, samudra, peene ka paani kuch na hota.
- Aag ka khatra: hydrogen jalti hai aur oxygen jalne mein madad karti hai. Aisa mixture ek chingaari se dhamaake ke saath jal sakta tha. Aag bujhana toh door, aag lagti!
- Banaavat badalti rehti: mixture ka anupaat fixed nahi hota, toh har jagah ka “paani” alag hota.
- Jeevan mushkil: paudhe, jaanwar aur hum sab ko liquid paani chahiye. Aisi duniya mein jeevan lagbhag namumkin hota.
Isse samajh aata hai ki compound banna kitna zaroori hai: do khatarnaak gas mil kar jeevan dene wala paani banati hain!
Q10 Loha choorn par dilute hydrochloric acid daalne se Gas A nikalti hai. Gas A pehchaano aur word equation likho.
Gas A = Hydrogen.
Word equation: Loha (iron) + Hydrochloric acid → Iron chloride + Hydrogen
Pehchaan: is gas ki koi gandh nahi hoti. Teacher jab test tube ke muh ke paas jalti teeli laate hain, toh halki “pop” ki awaaz aati hai, jo hydrogen ki pehchaan hai.
Agar loha ki jagah iron sulfide liya jaata, toh sade ande jaisi gandh wali hydrogen sulfide gas nikalti. Isi farq se mixture aur compound pehchaante hain.
Q11 Do aise compounds ke naam batao jo sirf non-metals se bane hon, aur har ek ke do upyog likho.
1. Paani (hydrogen + oxygen, dono non-metal)
- Peene, khaana banane aur saaf-safai mein.
- Kheti mein sinchaai aur aag bujhane mein.
2. Carbon dioxide (carbon + oxygen, dono non-metal)
- Paudhe ise prakash sanshleshan (photosynthesis) mein khaana banane ke liye lete hain.
- Soda/cold drink mein bulbule aur kuch fire extinguishers mein aag bujhane ke liye.
Aur bhi sahi jawaab: glucose (carbon, hydrogen, oxygen): sharir ko turant urja, aur ORS/drip mein. Ammonia (nitrogen + hydrogen): khaad (fertilizer) banane mein.
Q12 Sona ek mineral bhi hai aur metal bhi. Kaise?
Mineral kyun: sona dharti mein prakritik roop se, thos avastha mein aur fixed banaavat (sirf gold atom) ke saath milta hai. Yeh teeno mineral ki shartein hain. Kyunki yeh shuddh element ke roop mein milta hai, ise native mineral kehte hain.
Metal kyun: sona chamakdaar hai, peet kar patli parat banaya ja sakta hai, taar khincha ja sakta hai, aur garmi-bijli chalata hai. Yeh metal ke gun hain.
“Mineral” batata hai ki sona kahan aur kaise mila; “metal” batata hai ki uske gun kaise hain. Dono pehchaan ek saath sahi hain.
🖼️ Diagrams: Picture se Samjho
🔐 Deep Concept: Exam ke Chhupe Jaal
1. “Option mein ek bhi galat toh poora option galat.” Q4 ke option (ii) mein teen udaaharan sahi the, sirf “minerals” galat tha. Phir bhi option galat. MCQ mein har ek shabd jaancho.
2. Assertion–Reason ka do-step tareeka. Pehle A aur R ko alag-alag sach/jhooth jaancho. Dono sach hon, tab poochho: “Kya R batata hai ki A kyun sach hai?” Haan → (a/i), nahi → (b/ii). Q2 mein R, mixture ki paribhasha hai, isliye woh A ko samjhata hai.
3. Molecule ka matlab compound nahi. O₂, N₂, H₂ molecule hain, par ek hi element ke atom se bane hain, isliye element hain. Compound ke liye alag-alag elements chahiye (H₂O, CO₂).
4. Zang (rust) ki baarik baat. Zang loha, oxygen aur paani ki bhaap ke reaction se banta hai. Class 8 ke level par ise iron oxide yaani compound maana jaata hai. (Badi class mein padhoge ki isme paani ke kan bhi jude hote hain.)
5. Word equation ke niyam. Baayein taraf reactants (jo shuru mein the), daayein taraf products (jo bane), beech mein teer (→). Agar garam kiya, toh teer ke upar “garam” likho. Plus (+) ka matlab “aur”, barabar (=) mat lagao.
Toot nahi sakta → Element
Toot sakta + fixed anupaat + naye gun → Compound
Bas mile hue + apne gun + anupaat kuch bhi → Mixture
✏️ Examples: Naye Padarth, Wahi Chaabi
| Padarth | Group | Ek line ka kaaran |
|---|---|---|
| Chaandi (silver) | Element | Ek tarah ke atom; aur saral nahi hota |
| Cheeni (sugar) | Compound | Garam karne par carbon aur paani mein toot-ti hai |
| Nimbu-paani | Uniform mixture | Paani, cheeni, namak, nimbu ras; anupaat apni marzi |
| Poha-namkeen | Non-uniform mixture | Har cheez alag dikhti hai |
| Stainless steel | Uniform mixture (alloy) | Loha, chromium, nickel aur thoda carbon mile |
| Quartz | Compound (mineral) | Silicon aur oxygen fixed anupaat mein |
| Mercury (paara) | Element | Ek hi tarah ke atom; kamre ke taapmaan par liquid metal |
⚖️ Difference Table: Element vs Compound vs Mixture
| Baat | Element | Compound | Mixture |
|---|---|---|---|
| Kan | Ek tarah ke atom | Ek tarah ke molecule (alag elements jude) | Do ya zyada tarah ke kan |
| Banaavat | Fixed | Fixed | Badal sakti hai |
| Gun | Apne | Naye, elements se alag | Har hissa apne gun rakhta hai |
| Todna/alag karna | Aur saral nahi | Sirf chemical tareeke se | Bhautik tareeke se (magnet, chhanna) |
| Pure substance? | Haan | Haan | Nahi |
| Udaaharan | Loha, oxygen | Paani, namak | Hawa, brass, ret |
🚫 Misconceptions: Log aisa sochte hain… lekin
✅ Dono chemically fixed anupaat mein jude hain aur paani ke gun naye hain. Paani compound hai.
✅ Hawa uniform mixture hai; ek jaisa dikhna pure hone ka saboot nahi.
✅ Yeh alloys hain, yaani uniform mixtures. Inke metals ka anupaat badla ja sakta hai.
✅ Dono atom oxygen ke hain; ek hi element ka molecule element hi hai.
✅ Rock mixture hai, par mineral ki banaavat fixed hoti hai, isliye mineral pure substance hai.
✅ Reaction mein teer (→) lagta hai, jo batata hai ki reactants se products bane.
🔤 Key Terms (Exam mein English shabd hi likhna)
❓ FAQs
Exam mein Q6 jaisi lambi table kaise yaad karein?
Ratne ki zaroorat nahi. Har padarth par flowchart (Diagram 1) ke teen sawaal lagao. Pehle elements chhaanto (jo periodic table mein naam se milte hain: aluminium, sona…), phir “ek naam par kai elements” wale compounds, aur baaki mixtures.
Q2 mein option (i) likhein ya (a)?
Book mein jo numbering di hai wahi likho. NCERT book mein yahan (i), (ii)… hai; kai sample papers mein (a), (b)… hota hai. Matlab same hai.
Q10 mein “iron chloride” likhna kaafi hai?
Haan, Class 8 ke liye “Loha + hydrochloric acid → iron chloride + hydrogen” poora sahi hai. Badi class mein iska poora naam aur formula seekhoge.
Kya ret ko compound likh sakte hain kyunki quartz SiO₂ hai?
Shuddh quartz compound hai, par aam ret mein quartz ke saath doosre minerals, mitti aur kankad bhi hote hain. Isliye ret ko mixture likho.
Q11 mein kaun se compounds sabse safe jawaab hain?
Paani (H₂O) aur carbon dioxide (CO₂). Dono mein sirf non-metals hain aur dono ke upyog roz dikhte hain.
🧪 Activity: Loha + Sulfur, Mixture se Compound tak
Q7 aur Q10 ka asli aadhaar chapter ki woh activity hai jisme loha choorn aur sulfur powder pehle mila kar dekhe jaate hain, phir garam kiye jaate hain. Yahan use apne shabdon mein step-by-step samjhte hain.
Saamaan (lab mein): loha choorn, sulfur powder, magnet, kaagaz, china dish, burner, dilute hydrochloric acid, test tubes.
👀 Nateeja aur kyun? (Click karo)
| Kya dekha | Matlab |
|---|---|
| Garam karne se pehle loha magnet se khincha | Mixture mein har padarth apne gun rakhta hai |
| Garam karne ke baad naya kaala padarth, magnet ka asar nahi | Naya compound (iron sulfide) bana, naye gun ke saath |
| Acid se alag-alag gas | Mixture aur compound chemically alag padarth hain |
Is activity se kya seekha? Garam karne se padarth ke bas “mile hone” ki jagah “jud jaana” hota hai, aur tabhi compound banta hai.
Yeh activity NCERT ki Class 8 Science book Curiosity (Chapter 8) par aadharit hai, aur yahan apne shabdon mein samjhayi gayi hai.
🏠 Mini Experiments (Ghar pe)
⚠️ Safety Notes
🧠 Think Like a Scientist
🌍 Real Life Mein Chapter 8
- Rasoi: namak aur cheeni compound, masaala aur chutney mixtures, steel ke bartan alloy.
- Zang se bachaav: loha nam hawa se zang (compound) banata hai, isliye gate aur grill par paint karte hain.
- Aag bujhana: paani aur carbon dioxide aag bujhate hain, jabki inke elements (hydrogen, oxygen) jalne se jude hain.
- Hospital: glucose ki drip aur oxygen cylinder; ek compound, ek element.
- Kala aur sanskriti: Dhokra kala mein pighla brass ya bronze (alloys) use hota hai.
🔁 Recap: Poora Chapter Ek Nazar Mein
- Padarth do tarah: pure substance (element, compound) aur mixture (uniform, non-uniform).
- Element aur saral nahi hota (loha, oxygen); compound mein elements fixed anupaat mein jude hote hain aur naye gun aate hain (paani, namak).
- Mixture mein hisse apne gun rakhte hain aur bhautik tareeke se alag hote hain (hawa, ret, brass).
- Loha + sulfur → (garam) → iron sulfide; magnet ka asar nahi, acid se hydrogen sulfide.
- Loha + hydrochloric acid → iron chloride + hydrogen (“pop” test).
- Ek padarth element aur compound dono nahi ho sakta.
- Sona native mineral bhi hai aur metal bhi.
✍️ Fill in the Blanks
1. Jise chemical tareeke se aur saral padarthon mein toda na ja sake, use ______ kehte hain.
element
2. Paani mein hydrogen aur oxygen atomon ka anupaat ______ hai.
2:1
3. Loha aur sulfur ko garam karne par ______ banta hai.
iron sulfide
4. Loha dilute hydrochloric acid se ______ gas deta hai.
hydrogen
5. Hawa ek ______ mixture hai.
uniform
6. Shuddh element ke roop mein milne wale mineral ko ______ mineral kehte hain.
native
✅ True / False
1. Compound ke gun uske elements jaise hi hote hain.
False: compound ke gun naye hote hain; paani aag bujhata hai, hydrogen jalti hai.
2. Iron sulfide magnet ki taraf khinchta hai.
False: compound banne ke baad loha ka magnet wala gun nahi dikhta.
3. Carbon dioxide sirf non-metals se bana compound hai.
True: carbon aur oxygen dono non-metal hain.
4. Brass ek non-uniform mixture hai.
False: brass (tamba + jasta) alloy hai, yaani uniform mixture.
5. Saare pure substances ya toh element hote hain ya compound.
True: pure substance ke yahi do prakar hain.
6. Mixture ki banaavat hamesha fixed hoti hai.
False: mixture mein anupaat badal sakta hai; fixed banaavat pure substance ki pehchaan hai.
🔘 MCQs
Q1. Inme se kaun sa compound hai? (a) Hawa (b) Sona (c) Magnesium oxide (d) Samudri paani
✅ (c) Magnesium oxide: magnesium aur oxygen fixed anupaat mein jude.
(a) hawa gason ka mixture hai.
(b) sona element hai.
(d) samudri paani namak aur paani ka mixture hai.
Q2. Iron sulfide par dilute acid daalne se kaun si gas nikalti hai? (a) Hydrogen (b) Oxygen (c) Hydrogen sulfide (d) Carbon dioxide
✅ (c) Hydrogen sulfide: sade ande jaisi gandh.
(a) hydrogen loha (mixture wale) se nikalti hai, iron sulfide se nahi.
(b) oxygen is reaction mein nahi banti.
(d) carbon dioxide ke liye carbon wala padarth chahiye, jaise baking soda.
Q3. Kaun sa jodd sirf elements ka hai? (a) Paani, oxygen (b) Nitrogen, sulfur (c) Namak, loha (d) Glucose, hydrogen
✅ (b) Nitrogen, sulfur: dono elements.
(a) paani compound hai.
(c) namak compound hai.
(d) glucose compound hai.
Q4. Kaun sa non-uniform mixture hai? (a) Brass (b) Hawa (c) Keechad wala paani (d) Cheeni ka ghol
✅ (c) Keechad wala paani: mitti ke kan alag dikhte aur neeche baithte hain.
(a) brass uniform alloy hai.
(b) hawa uniform hai.
(d) cheeni ka ghol uniform hai.
Q5. Hawa mein sabse zyada kaun si gas hai? (a) Oxygen (b) Nitrogen (c) Carbon dioxide (d) Argon
✅ (b) Nitrogen: lagbhag 78%.
(a) oxygen lagbhag 21%, doosre number par.
(c) carbon dioxide bahut kam.
(d) argon 1% se bhi kam.
Q6. Paani ka compound hona kis baat se pakka hota hai? (a) Woh rangheen hai (b) Bijli guzaarne par hydrogen aur oxygen mein toot-ta hai (c) Woh liquid hai (d) Woh bahta hai
✅ (b): chemical tareeke se do elements mein todna compound ki pehchaan hai.
(a) rangheen toh hawa bhi hai, jo mixture hai.
(c) liquid hona group nahi batata (mercury element bhi liquid hai).
(d) bahna bhi har liquid ka gun hai.
Q7. Sona mineral kyun hai? (a) Woh mehnga hai (b) Woh prakritik, thos aur fixed banaavat wala hai (c) Woh chamakta hai (d) Woh gehnon mein lagta hai
✅ (b): yahi mineral ki teen shartein hain.
(a) keemat se group tay nahi hota.
(c) chamak metal ka gun hai, mineral ki shart nahi.
(d) upyog se mineral nahi banta.
Q8. “Loha + sulfur → iron sulfide” mein reactant kaun hain? (a) Sirf iron sulfide (b) Loha aur sulfur (c) Sirf loha (d) Iron sulfide aur sulfur
✅ (b) Loha aur sulfur: teer ke baayein taraf wale reactants hain.
(a) iron sulfide product hai.
(c) sulfur bhi reactant hai, sirf loha nahi.
(d) iron sulfide product hai, reactant nahi.
🔗 Assertion–Reason
Options: (a) A aur R dono sahi, aur R, A ko samjhata hai · (b) A aur R dono sahi, par R, A ko nahi samjhata · (c) A sahi, R galat · (d) A galat, R sahi
1. A: Iron sulfide ko magnet se loha aur sulfur mein alag nahi kar sakte. R: Iron sulfide mein loha aur sulfur chemically jude hain.
✅ (a): chemical jod hi wajah hai ki bhautik tareeka (magnet) kaam nahi karta.
2. A: Oxygen gas ek compound hai. R: Oxygen ke molecule mein do atom hote hain.
✅ (d): A galat, oxygen element hai kyunki dono atom oxygen ke hain. R sahi hai.
3. A: Samudri paani ek mixture hai. R: Samudri paani ka swaad khaara hota hai.
✅ (b): dono sahi, par khaara swaad mixture hone ka kaaran nahi. Asli kaaran: namak aur paani bina fixed anupaat ke mile hain aur bhaap bana kar namak alag ho jaata hai.
📝 Very Short Answer (1 mark)
1. Pure substance ke do prakar batao.
Element aur compound.
2. Ek uniform mixture ka udaaharan do.
Hawa (ya brass, namak ka ghol).
3. Hydrogen gas ki pehchaan kaise hoti hai?
Jalti teeli paas laane par “pop” ki awaaz.
4. Kamre ke taapmaan par liquid rehne wale do elements?
Mercury (metal) aur bromine (non-metal).
5. Brass kin metals se banta hai?
Tamba (copper) aur jasta (zinc).
🗒️ Short Answer (2–3 marks)
1. Mixture aur compound mein teen antar likho.
(i) Mixture mein anupaat badal sakta hai, compound mein fixed. (ii) Mixture ke hisse apne gun rakhte hain, compound ke gun naye hote hain. (iii) Mixture bhautik tareeke se alag hota hai, compound sirf chemical tareeke se.
2. Cheeni ko compound kyun kehte hain?
Garam karne par cheeni carbon (kaala padarth) aur paani mein toot jaati hai. Yaani usme carbon, hydrogen aur oxygen chemically jude hain, isliye woh compound hai.
3. Hawa mixture hai, yeh kaise pata chalta hai? Do kaaran do.
(i) Hawa ki gas apne gun rakhti hain: oxygen jalne mein madad karti hai, carbon dioxide chuna-paani ko doodhiya karti hai. (ii) Hawa ki banaavat jagah-jagah thodi badalti hai (jaise paani ki bhaap), fixed nahi.
4. Stainless steel shuddh loha se behtar kyun hai?
Stainless steel loha, chromium, nickel aur thode carbon ka alloy hai. Yeh shuddh loha se zyada mazboot aur tikau hai, aur jaldi zang nahi khaata. Isliye bartan aur auzaar isse bante hain.
📄 Long Answer (5 marks)
1. Loha choorn aur sulfur ke mixture ko garam karne ki activity samjhao. Garam karne se pehle aur baad ke farq likho, aur word equation do.
Pehle loha choorn aur sulfur powder mila kar mixture banaya jaata hai. Isme grey loha aur peela sulfur alag dikhte hain, aur magnet se loha alag ho jaata hai. Teacher is mixture ko garam karte hain; woh laal chamakta hai aur thanda hone par kaala-bhoora thos, iron sulfide, ban jaata hai.
Word equation: Loha + Sulfur —(garam)→ Iron sulfide.
Farq: (1) Pehle magnet loha ko kheenchta hai, baad mein nahi. (2) Pehle hisse alag dikhte hain, baad mein ek jaisa padarth. (3) Dilute acid se pehle hydrogen (bina gandh), baad mein hydrogen sulfide (sade ande ki gandh). (4) Pehle anupaat kuch bhi, baad mein fixed. (5) Pehle bhautik tareeke se alag, baad mein nahi.
Nishkarsh: garam karne se chemical badlav hua aur naya compound bana.
2. Element, compound aur mixture ko paribhasha, do-do udaaharan aur ek-ek pehchaan ke saath samjhao. Pure substance kaun hain?
Element: jise chemical tareeke se aur saral na kiya ja sake; ek tarah ke atom. Udaaharan: loha, oxygen. Pehchaan: kisi bhi reaction se aur toot-ta nahi.
Compound: do ya zyada elements fixed anupaat mein chemically jude; naye gun. Udaaharan: paani, sodium chloride. Pehchaan: chemical tareeke se elements mein toot-ta hai (paani bijli se).
Mixture: do ya zyada padarth bina chemical jod ke mile; anupaat kuch bhi. Udaaharan: hawa, ret. Pehchaan: bhautik tareeke se alag ho jaata hai.
Pure substance: element aur compound dono, kyunki inki banaavat fixed hai. Mixture pure substance nahi.
📰 Case-Based Question
Priya ki school lab mein teacher ne chaar bottles rakhi jin par label tha: P = “chamakdaar laal-bhoora metal ke taar”, Q = “safed crystal jo garam karne par kaale ho kar paani ki boondein dete hain”, R = “neela ghol jisme paani aur ek namak mila hai, kitna bhi mila sakte hain”, S = “ek safed thos jo tez garam karne par toot kar ek gas aur ek naya safed thos deta hai”. Teacher ne kaha: “P ko kisi bhi tareeke se aur saral nahi kiya ja saka.”
Q1. P kis group mein hai? Kyun?
Element (laal-bhoore taar, shayad tamba), kyunki use aur saral nahi kiya ja saka.
Q2. Q kaun sa padarth ho sakta hai aur kis group mein?
Cheeni jaisa compound; garam karne par carbon (kaala) aur paani mein toot gaya, isliye compound.
Q3. R mixture kyun hai, aur kaun sa prakar?
Paani aur namak bina fixed anupaat ke mile hain (“kitna bhi”), isliye mixture. Ghol ek jaisa dikhta hai, isliye uniform mixture.
Q4. Kya S element ho sakta hai?
Nahi. Jo thos garam karne par toot kar do naye padarth (gas aur doosra thos) de, use aur saral kiya ja saka, isliye woh element nahi; woh compound hai.
🚀 HOTS (Higher Order Thinking)
1. Ek padarth ko garam karne par woh pighalta hai aur thanda karne par wahi padarth wapas mil jaata hai. Kya isse pata chalta hai ki woh compound hai?
Nahi. Pighalna sirf avastha ka badlav hai; koi naya padarth nahi bana. Element (jaise tin), compound (jaise barf) ya mixture (jaise mom), koi bhi pighal sakta hai. Compound pakka karne ke liye dekhna padega ki kya woh chemical tareeke se naye padarthon mein toot-ta hai.
2. Ek bachcha kehta hai: “Namak mein chlorine hai jo zehreeli gas hai, toh namak khaana khatarnaak hai.” Uski galti samjhao.
Namak (sodium chloride) compound hai, jisme sodium aur chlorine chemically jude hain. Compound ke gun elements se alag hote hain, isliye namak zehreela nahi, sahi matra mein zaroori hai. Q3 wali baat yahan bhi lagti hai.
3. Do sample hain: ek mein loha aur sulfur 1:1 vazan mein, doosre mein 3:1. Dono ko sirf mila kar rakha hai. Kya dono ek hi padarth hain?
Dono loha aur sulfur ke mixtures hain, par anupaat alag hai, isliye gun thode alag (rang, magnet ka asar) honge. Mixture mein anupaat kuch bhi ho sakta hai. Compound (iron sulfide) mein anupaat hamesha fixed hota, isliye har sample ek jaisa hota.
🏆 Olympiad Corner
1. Kaun sa jodd sahi hai? (a) Bronze: tamba + jasta (b) Brass: tamba + tin (c) Bronze: tamba + tin (d) Stainless steel: loha + sona
✅ (c): bronze (kaansa) tamba aur tin ka alloy hai. (a) aur (b) mein jasta aur tin ulat gaye; brass tamba + jasta hai. (d) stainless steel mein sona nahi, chromium aur nickel hote hain.
2. Kamre ke taapmaan par kitne elements gas hote hain, aur woh metal hain ya non-metal?
11 elements gas hote hain, aur saare non-metal hain (jaise hydrogen, oxygen, nitrogen, helium).
3. Kaun sa element haath ki garmi (lagbhag 30 °C) par pighal sakta hai? (a) Loha (b) Gallium (c) Sulfur (d) Carbon
✅ (b) Gallium: lagbhag 30 °C par pighalta hai. (a) loha bahut zyada taapmaan par pighalta hai. (c) sulfur ko 100 °C se zyada chahiye. (d) carbon (graphite/heera) bahut kathin se pighalta hai.
📚 Aur Padho (External Reference)
- NCERT Class 8 Science Curiosity, Chapter 8 (official PDF): chapter ke end mein “Keep the curiosity alive” wale poore sawaal dekho
- DIKSHA: Sarkar ka free learning platform, NCERT ke videos ke liye
💖 CharuMam Motivation
Badhai ho! Aapne poora Chapter 8 khatam kar liya. 🎉 Yaad hai Q9? Hydrogen akele jalti hai, oxygen akele aag bhadkaati hai, par dono sahi tarah jud jaayein toh paani banta hai, jo jeevan deta hai.
Hum bhi aise hi hain, beta. Akele mein shayad hum jaldi gussa ho jaate hain ya jaldi haar maan lete hain, par achhe dost, parivaar aur mehnat ke saath jud kar hum kuch bilkul naya aur sundar ban jaate hain. Aaj ek kaam karo: chapter ke 12 sawaal bina dekhe kisi dost ko samjhao. Jo samjha sake, wahi asli seekha! 🌱
— CharuMam
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