NCERT Exercise Solutions
Chapter 9 ke saare 12 sawaal: solution, solubility, mass, volume aur density. Har jawaab poore kaaran aur hisaab ke saath! 📘✅
🧭 Is Post Mein
📖 Kahani: Santra Kyun Doob Gaya?
Ravivaar ki dopahar. Golu, Priya aur Rohan chapter 9 ka exercise karne baithe. Table par ek glass paani, ek santra, ek chhota pathar aur rasoi ka weighing scale pada tha.
Golu ne poora santra paani mein daala. Santra tairne laga. Phir usne santra chheel kar dobara daala, aur is baar woh neeche baith gaya! “Arre! Chhilka utaarne se santra bhaari ho gaya kya?”
Priya hansi: “Bhaari nahi hua, halka hi hua hai! Chhilke ke saath toh mass zyada tha. Baat mass ki nahi, density ki hai.”
Rohan ne pathar uthaya: “Aur yeh pathar 225 gram ka hai, volume 90 cm³. Hisaab lagaayein toh bina paani mein daale bata sakte hain ki doobega ya tairega.”
Teeno samajh gaye ki chapter ke saare sawaal kuch hi chaabiyon se khulte hain: solution ki pehchaan, solubility, aur density = mass ÷ volume. Aaj hum inhi chaabiyon se NCERT ke saare 12 sawaal step-by-step solve karenge. 🔑
🎯 Is Post Mein Kya Seekhenge
- Chapter 9 ke end ke saare 12 exercise sawaalon ke poore, kaaran wale jawaab
- Solution, saturated aur unsaturated solution ko sahi pehchaanna
- Garmi ka solids aur gases ki solubility par asar
- Density ke sawaal 4 step mein: likho, formula, hisaab, unit
- Tairna ya doobna: 1 g/cm³ wali chaabi, aur garmi ka density par asar
🧱 Basics: Pehle Yeh Aana Chahiye
1. Solution: solute (jo ghulta hai) + solvent (jisme ghulta hai) ka uniform mixture. (Post 1: Solution Kya Hai?)
2. Saturated / unsaturated: kisi taapmaan par aur solute na ghule toh saturated, ghul sake toh unsaturated. (Post 2)
3. Solubility aur taapmaan: garam paani mein zyadatar solids zyada ghulte hain, par gases kam. (Post 3, Post 4)
4. Density: density = mass ÷ volume; paani se kam density tairti hai, zyada doobti hai. (Post 5, Post 6, Post 7, Post 8)
5. Maths ki taiyaari: bhaag aur decimal mein jawaab aayega (jaise 75.95). Decimal ko theek se padhna seekhne ke liye dekho Maths ki Neev MN-03: Decimal Point ka asli matlab, aur “lagbhag 76” bolna MN-05: Rounding se.
💡 Concept: Har Sawaal ki Chaabi
Chapter 9 ke sawaal do tarah ke hain: solution wale aur density wale. Dono ke liye ek-ek chaabi:
Density = Mass ÷ Volume
Mass = Density × Volume
Volume = Mass ÷ Density
Jo nikalna hai use chhupao, baaki do ka rishta dikh jaayega. Q11 mein isi teesre roop ki zaroorat 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 Paanch kathan sahi (T) hain ya galat (F)? Galat waalon ko sudhaaro: (i) oxygen garam paani mein thande se zyada ghulti hai (ii) ret + paani ek solution hai (iii) cheez dwara gheri gayi jagah ko mass kehte hain (iv) unsaturated solution mein saturated se zyada solute ghula hota hai (v) vayumandal ki gason ka mixture bhi ek solution hai
| Kathan | T/F | Sahi roop aur kaaran |
|---|---|---|
| (i) | F | Oxygen thande paani mein zyada ghulti hai. Garmi se gas ke kan tez bhaagte hain aur paani se bahar nikal jaate hain. |
| (ii) | F | Ret + paani non-uniform mixture hai, solution nahi. Ret ghulti nahi aur neeche baith jaati hai. |
| (iii) | F | Gheri gayi jagah ko volume kehte hain. Mass matlab cheez mein kitna padarth (matter) hai. |
| (iv) | F | Utne hi solvent aur usi taapmaan par, saturated solution mein zyada (sabse zyada mumkin) solute ghula hota hai; unsaturated mein kam. |
| (v) | T | Hawa mein nitrogen (solvent jaisa, sabse zyada) mein oxygen, argon, carbon dioxide aadi ek jaise ghule-mile hain. Yeh gas ka uniform mixture yaani solution hai. |
Q2 Khaali jagah bharo: (i) displacement method mein thos ko paani mein ____ karte hain aur paani ke level mein ____ naapte hain (ii) kisi taapmaan par ____ ki woh sabse zyada maatra jo ____ mein ghul sake, solubility kehlaati hai (iii) aam taur par taapmaan badhne par density ____ hai (iv) jis solution mein us taapmaan par aur glucose na ghule, woh glucose ka ____ solution hai
- (i) poori tarah duba (immerse); badhat (rise)
- (ii) solute; solvent
- (iii) ghat-ti (decreases)
- (iv) saturated
(i) ka kaaran: thos jitni jagah gherta hai, utna paani upar uthta hai. Isliye level ki badhat = thos ka volume. (iii) ka kaaran: garmi se cheez phailti hai, volume badhta hai, mass wahi rehta hai, toh mass ÷ volume chhota ho jaata hai.
Q3 Paani ke glass mein tel daalne par tel upar tairta hai. Isse kya pata chalta hai? (i) tel paani se zyada dense (ii) paani tel se zyada dense (iii) dono ki density barabar (iv) tel paani mein ghul jaata hai
✅ Option (ii): paani, tel se zyada dense hai.
- (i) galat: zyada dense cheez neeche jaati, upar nahi tairti.
- (iii) galat: density barabar hoti toh tel upar na aata, paani ke beech mein kahin bhi tika reh sakta tha.
- (iv) galat: tel ghulta toh alag parat dikhti hi nahi; tel aur paani alag rehte hain.
Q4 Ek pathar ki murti ka mass 225 g aur volume 90 cm³ hai. Density nikaalo aur batao paani mein tairegi ya doobegi.
Diya hai: mass = 225 g, volume = 90 cm³
Formula: density = mass ÷ volume
Hisaab: 225 ÷ 90 = 2.5 g/cm³ (225 ÷ 9 = 25, phir 25 ÷ 10 = 2.5)
Nateeja: 2.5 g/cm³ paani ki density (1 g/cm³) se zyada hai, isliye murti doob jaayegi.
Q5 Sabse sahi kathan chuno aur baaki galat kyun hain, batao: (i) saturated solution us taapmaan par aur solute ghol sakta hai (ii) unsaturated solution ne sabse zyada solute ghol liya hai (iii) us taapmaan par saturated solution mein aur solute nahi ghul sakta (iv) saturated solution sirf zyada taapmaan par banta hai
✅ Option (iii) saturated solution ki sahi paribhasha hai.
- (i) galat: “aur ghol sakta hai” toh unsaturated ki pehchaan hai.
- (ii) galat: sabse zyada solute ghula ho toh woh saturated kehlaata hai, unsaturated nahi.
- (iv) galat: saturated solution kisi bhi taapmaan par ban sakta hai, thande paani mein bhi. Bas har taapmaan par “kitna ghulega” ki seema alag hoti hai.
Q6 2 litre ki bottle mein 500 mL paani daala. Ab usme aur kitna paani aa sakta hai?
Step 1, ek unit mein lao: 1 L = 1000 mL, toh 2 L = 2000 mL.
Step 2, ghatao: 2000 mL − 500 mL = 1500 mL, yaani 1.5 litre.
Galti se bacho: 2 − 500 mat karna! Pehle dono ko mL mein badlo, phir ghatao.
Q7 Ek cheez ka mass 400 g aur volume 40 cm³ hai. Density kitni hai?
Density = 400 g ÷ 40 cm³ = 10 g/cm³.
Matlab is cheez ka har 1 cm³ hissa 10 gram ka hai. Paani (1 g/cm³) se 10 guna dense, isliye yeh paani mein doobegi.
Q8 (Chitra par aadharit) Chhilke wala santra paani mein tairta hai, par chheela hua santra doob jaata hai. Kyun?
Santre ke chhilke mein bahut saare chhote-chhote hawa ke khaane (air pockets) hote hain. Chhilka halka aur spongy hota hai, isliye uski density kam hoti hai.
- Chhilke ke saath: hawa bhara chhilka santre ka volume kaafi badha deta hai par mass thoda hi. Poore santre ki density paani se kam ho jaati hai → tairta hai. Chhilka “life jacket” jaisa kaam karta hai.
- Chheelne ke baad: hawa wala hissa hat gaya. Andar ka gooda (rasila hissa) paani se thoda zyada dense hai → doob jaata hai.
Dhyaan do: chheelne se mass kam hua, phir bhi santra dooba. Toh tairna-doobna mass se nahi, density se tay hota hai.
Q9 Cheez A: mass 200 g, volume 40 cm³. Cheez B: mass 240 g, volume 60 cm³. Kaun zyada dense hai?
| Cheez | Mass | Volume | Density = mass ÷ volume |
|---|---|---|---|
| A | 200 g | 40 cm³ | 200 ÷ 40 = 5 g/cm³ |
| B | 240 g | 60 cm³ | 240 ÷ 60 = 4 g/cm³ |
Jawaab: A zyada dense hai (5 > 4), jabki B ka mass zyada hai.
Yahi jaal hai: “B bhaari hai toh B dense” sochna galat. Density ka matlab hai har 1 cm³ mein kitna mass.
Q10 Reema 120 g clay se 60 cm³ ka cube banati hai, phir use dabaa kar patli sheet bana deti hai. Density ka kya hoga?
Cube ki density: 120 ÷ 60 = 2 g/cm³.
Sheet banane par: na clay joda gaya, na nikala gaya, toh mass 120 g hi raha. Clay ko sirf naya aakaar mila, dabaane se uska volume bhi 60 cm³ hi raha (clay ke andar se hawa nahi nikli maan kar). Isliye density = 120 ÷ 60 = 2 g/cm³, bilkul wahi.
Niyam: shape badalne se density nahi badalti. Density padarth ki pehchaan hai, aakaar ki nahi.
Q11 Loha ke ek block ka mass 600 g aur density 7.9 g/cm³ hai. Iska volume kitna hai?
Formula ulta karo: volume = mass ÷ density
Hisaab: 600 ÷ 7.9 = 6000 ÷ 79 ≈ 75.95 cm³, yaani lagbhag 76 cm³.
Check: 7.9 × 76 = 600.4 g, jo 600 g ke bahut paas hai. Isliye jawaab sahi hai. (Decimal se bachne ke liye 600 aur 7.9 dono ko 10 se guna kiya: 6000 ÷ 79.)
Q12 (Chitra par aadharit) Paani bhari test tube, jisme ek patli glass tube lagi hai, lagbhag 70 °C ke garam paani mein rakhi. Glass tube mein paani ka level upar chadh gaya. Paani ki density par kya asar hua?
Kya hua: garam hone par test tube ka paani phail gaya (expand hua). Uska volume badha, aur badha hua paani patli tube mein upar chadh gaya.
Mass: na paani joda, na nikala, toh mass wahi raha.
Density: mass same, volume zyada → density = mass ÷ volume ghat gayi.
Isi wajah se garam paani thande paani ke upar aata hai, aur aam taur par garmi se cheezon ki density kam hoti hai (Q2 (iii) bhi yahi kehta hai).
🖼️ Diagrams: Picture se Samjho
🔐 Deep Concept: Exam ke Chhupe Jaal
Yeh hissa sirf charumam.com readers ke liye 🔐
1. Unit ka jaal. Volume litre mein aur mass gram mein diya ho, toh pehle litre ko mL (= cm³) mein badlo. 1 L = 1000 mL = 1000 cm³. Q6 jaisa sawaal isi mein galti karwata hai.
2. “Bhaari = dense” ka jaal. Q9 mein B ka mass zyada tha, par density A ki zyada thi. Hamesha har 1 cm³ ka mass socho.
3. Shape ka jaal. Q10: aakaar badalne se mass aur volume dono wahi rehte hain, toh density bhi wahi. Lekin agar cheez ke andar hawa bhar di jaaye (jaise clay ki kishti ya steel ka jahaz), toh poori cheez ki ausat density ghat jaati hai, padarth ki nahi.
4. Saturated ka taapmaan wala jaal. “Saturated” hamesha kisi khaas taapmaan par hota hai. Thanda saturated cheeni ka ghol garam karo, toh woh unsaturated ban jaata hai aur aur cheeni ghol leta hai.
5. Gas ulta chalti hai. Solids ke liye garmi = zyada solubility, gases ke liye garmi = kam solubility. Q1 (i) isi ulte niyam ko parakhta hai.
6. Paani ka anokha vyavhaar. Aam niyam hai ki garmi se density ghat-ti hai, lekin paani 0 °C se 4 °C tak thoda sikudta hai; uski sabse zyada density lagbhag 4 °C par hoti hai. Isiliye barf (0 °C) paani par tairti hai. Exam mein “generally” (aam taur par) shabd isi wajah se likha hota hai.
D = M ÷ V | M = D × V | V = M ÷ D
D < 1 → tairo, D > 1 → doobo
Garmi ↑ → solid zyada ghule, gas kam ghule, density ghate
✏️ Examples: Naye Sawaal, Wahi Chaabi
⚖️ Difference Table: Chapter ke Jode
| Jodi | Pehla | Doosra |
|---|---|---|
| Solute vs Solvent | Solute: jo ghulta hai, aam taur par kam maatra (namak) | Solvent: jisme ghulta hai, aam taur par zyada maatra (paani) |
| Saturated vs Unsaturated | Us taapmaan par aur solute nahi ghulta | Us taapmaan par aur solute ghul sakta hai |
| Solid vs Gas ki solubility | Solid: garmi se aam taur par badhti hai | Gas: garmi se ghat-ti hai |
| Mass vs Volume | Mass: kitna padarth; gram/kg; balance se | Volume: kitni jagah; mL/L/cm³; measuring cylinder se |
| Solution vs Non-uniform mixture | Har jagah ek jaisa, kuch neeche nahi baithta (namak-paani) | Hisse alag dikhte, neeche baith sakte (ret-paani) |
| Tairna vs Doobna | Density paani se kam (< 1 g/cm³) | Density paani se zyada (> 1 g/cm³) |
🚫 Misconceptions: Log aisa sochte hain… lekin
✅ Bada lakdi ka latta bhaari hai par tairta hai; chhoti keel halki hai par doobti hai. Faisla density karti hai.
✅ Solids ke liye aam taur par haan, par gases (oxygen, CO₂) garam paani mein kam ghulti hain.
✅ Saturated matlab us taapmaan par aur solute nahi ghulega, chahe ghol patla dikhe.
✅ Mass aur volume wahi, toh density wahi. Sirf shape badla.
✅ Hawa gason ka solution hai, aur brass jaise alloy thos solution hain.
✅ Mass toh kam hua! Hawa bhara chhilka hatne se density badhi, isliye dooba.
🔤 Key Terms (Exam mein English shabd hi likhna)
❓ FAQs
Density ka unit g/cm³ likhein ya g/mL?
Dono sahi hain kyunki 1 mL = 1 cm³. Thos ke liye g/cm³ aur liquid ke liye g/mL zyada chalta hai. Bade padarthon ke liye kg/m³ bhi hota hai (paani = 1000 kg/m³).
Q11 mein 75.95 likhein ya 76?
Dono likh do: “≈ 75.95 cm³, yaani lagbhag 76 cm³”. Isse examiner ko dikhega ki aapne hisaab bhi kiya aur sahi rounding bhi ki.
Hawa solution kaise hai, usme toh koi liquid hi nahi?
Solution ke liye liquid zaroori nahi. Zaroori hai ki mixture har jagah ek jaisa ho. Hawa ki gases poori tarah aur barabar mili hoti hain, isliye hawa gas ka solution hai.
Q8 mein “air pockets” ki jagah kya likh sakte hain?
“Chhilke mein hawa bhare chhote khaane hote hain” ya “chhilka spongy hai aur usme hawa phansi hoti hai”. Saath mein density wali line zaroor likho: “isse poore santre ki density paani se kam ho jaati hai”.
Kya saare liquids garam karne par phailte hain?
Haan, aam taur par. Isi par thermometer ka mercury ya alcohol chalta hai. Paani 0–4 °C ke beech thoda alag vyavhaar karta hai, par Q12 mein 70 °C hai, wahan paani phailta hi hai.
🧪 Activity: Garam Paani mein Phailta Paani (Q12)
Q12 chapter ki us activity par bana hai jisme paani bhari test tube ko garam paani mein rakh kar dekha jaata hai ki paani ka volume aur density kaise badalte hain. Yahan use apne shabdon mein step-by-step samjhte hain.
Saamaan: ek test tube, ek chhed wala rubber cork, ek patli khokhli glass tube (ya saaf transparent straw, cork mein kas kar fit), rangeen paani, ek bada beaker ya steel ka bartan, garam paani, marker.
👀 Nateeja aur kyun? (Click karo)
| Kya dekha | Matlab |
|---|---|
| Garam karne par level upar chadha | Paani phaila, volume badha |
| Paani na joda na nikala | Mass wahi raha |
| Mass same, volume zyada | Density ghati (D = M ÷ V) |
| Thanda karne par level neeche | Volume ghata, density wapas badhi |
Is activity se kya seekha? Garmi se zyadatar padarth phailte hain, isliye aam taur par taapmaan badhne par density ghat-ti hai.
Yeh activity NCERT ki Class 8 Science book Curiosity (Chapter 9) 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 9
- Barf ka tairna: barf ki density paani se kam hai. Poori kahani: Science ki Neev SN-01.
- Lohe ka jahaz: loha dense hai, par jahaz ke andar hawa bhari jagah poore jahaz ki ausat density kam kar deti hai. Padho SN-04.
- Garmi mein machhliyan: garam talaab mein oxygen kam ghulti hai, isliye garmiyon mein machhliyan satah par saans lene aati hain.
- Cold drink: garam bottle kholne par zyada jhaag, kyunki garmi mein CO₂ kam ghulti hai.
- ORS aur chashni: ORS ek solution hai; chashni banaate waqt garam paani mein zyada cheeni ghulti hai.
- Rasoi ka mapna: 1 L ki bottle, 500 mL ka doodh packet: volume roz naapte hain.
🔁 Recap: Poora Chapter Ek Nazar Mein
- Solution = solute + solvent ka uniform mixture; hawa bhi solution hai, ret-paani nahi.
- Saturated: us taapmaan par aur solute nahi ghulta; unsaturated: ghul sakta hai.
- Solubility: kisi taapmaan par solvent mein ghul sakne wali solute ki sabse zyada maatra.
- Garmi se solids zyada ghulte hain, gases kam (oxygen thande paani mein zyada).
- Mass = padarth ki maatra; volume = gheri hui jagah; 1 L = 1000 mL; 1 mL = 1 cm³.
- Density = mass ÷ volume; paani ≈ 1 g/cm³; kam tairta, zyada doobta.
- Shape badalne se density nahi badalti; garmi se aam taur par density ghat-ti hai.
✍️ Fill in the Blanks
1. Namak-paani mein namak ______ hai aur paani ______ hai.
solute; solvent
2. Jis ghol mein us taapmaan par aur solute ghul sake, use ______ solution kehte hain.
unsaturated
3. Gases ki solubility taapmaan badhne par ______ hai.
ghat-ti (decreases)
4. 1 litre = ______ mL.
1000
5. Density = ______ ÷ ______.
mass; volume
6. Jis cheez ki density 1 g/cm³ se kam ho, woh paani mein ______ hai.
tairti (floats)
✅ True / False
1. Har solution liquid hi hota hai.
False: hawa gas ka solution hai, brass thos solution (alloy) hai.
2. Saturated solution ko garam karne par woh aur solute ghol sakta hai.
True: solids ki solubility garmi se aam taur par badhti hai, toh ghol unsaturated ban jaata hai.
3. Volume naapne ke liye weighing balance use karte hain.
False: balance se mass naapte hain; volume ke liye measuring cylinder ya displacement.
4. 5 g/cm³ density wali cheez paani mein doobegi.
True: 5 > 1, paani se zyada dense.
5. Lohe ki keel ko hathode se chapta karne par uski density badal jaati hai.
False: mass aur volume wahi, sirf shape badla; density wahi.
6. Garam karne par liquid phailta hai aur uski density aam taur par kam hoti hai.
True: volume badhta hai, mass wahi, toh mass ÷ volume chhota.
🔘 MCQs
Q1. Inme se solution kaun sa hai? (a) Ret aur paani (b) Chaak powder aur paani (c) Cheeni aur paani (d) Tel aur paani
✅ (c) Cheeni aur paani: cheeni poori ghul kar uniform mixture banati hai.
(a) ret ghulti nahi, neeche baith jaati hai.
(b) chaak powder paani ko dhundhla karta hai aur dheere-dheere neeche baith jaata hai; yeh solution nahi.
(d) tel ghulta nahi, upar alag parat banata hai.
Q2. Garmiyon mein talaab ki machhliyan satah par kyun aati hain? (a) Garam paani mein oxygen zyada ghulti hai (b) Garam paani mein oxygen kam ghulti hai (c) Paani ki density badh jaati hai (d) Unhe dhoop chahiye
✅ (b): gases garam paani mein kam ghulti hain, toh machhliyon ko oxygen kam milti hai.
(a) ulta hai; garmi se gas ki solubility ghat-ti hai.
(c) garmi se paani ki density badhti nahi, thodi ghat-ti hai; aur yeh saans ka kaaran nahi.
(d) dhoop ka saans se koi lena-dena nahi; asli kaaran oxygen ki kami hai.
Q3. 150 g mass aur 50 cm³ volume wali cheez ki density hai: (a) 3 g/cm³ (b) 0.33 g/cm³ (c) 200 g/cm³ (d) 7500 g/cm³
✅ (a) 3 g/cm³: 150 ÷ 50 = 3.
(b) volume ÷ mass (50 ÷ 150) kar diya, ulta formula.
(c) dono ko jod diya (150 + 50); density mein jodna nahi hota.
(d) dono ko guna kar diya (150 × 50).
Q4. Pathar ka volume nikaalne ka sabse sahi tareeka: (a) Ruler se lambai naapna (b) Balance par tolna (c) Measuring cylinder ke paani mein duba kar level ki badhat padhna (d) Haath se andaza lagana
✅ (c): displacement method; badhat = pathar ka volume.
(a) pathar ka aakaar aniyamit hai, ruler se volume nahi nikalta.
(b) balance mass batata hai, volume nahi.
(d) andaza science ka naap nahi hai.
Q5. Ek ghol mein us taapmaan par aur namak nahi ghul raha. Yeh ghol hai: (a) Unsaturated (b) Saturated (c) Non-uniform mixture (d) Shuddh paani
✅ (b) Saturated: aur solute na ghule, yahi paribhasha hai.
(a) unsaturated mein aur ghul sakta hai.
(c) ghula hua namak uniform mixture banata hai; neeche pada extra namak ghol ka hissa nahi.
(d) usme namak ghula hai, toh shuddh paani nahi.
Q6. 3 L ki baalti mein 1200 mL paani hai. Aur kitna paani aayega? (a) 1800 mL (b) 1197 mL (c) 4200 mL (d) 2800 mL
✅ (a) 1800 mL: 3000 − 1200 = 1800.
(b) 1200 − 3 kar diya, unit badle bina.
(c) jod diya (3000 + 1200).
(d) hisaab ki galti; 3000 − 1200 = 1800 hota hai, 2800 nahi.
Q7. Ek lakdi (density 0.6 g/cm³) ko do tukdon mein kaata. Har tukde ki density hogi: (a) 0.3 g/cm³ (b) 0.6 g/cm³ (c) 1.2 g/cm³ (d) 0 g/cm³
✅ (b) 0.6 g/cm³: mass aur volume dono aadhe hue, anupaat wahi.
(a) sirf mass aadha maana, volume bhi aadha hota hai.
(c) density kaatne se dugni nahi hoti.
(d) padarth hai toh density kabhi zero nahi.
Q8. Inme se kaun paani mein tairega? (a) Density 2.5 g/cm³ (b) Density 1.3 g/cm³ (c) Density 0.8 g/cm³ (d) Density 7.9 g/cm³
✅ (c) 0.8 g/cm³: 1 se kam, paani se halka (per cm³).
(a) 2.5 > 1, doobega (jaise Q4 ki murti).
(b) 1.3 > 1, dheere doobega.
(d) 7.9 > 1, loha jaisa, doobega.
🔗 Assertion–Reason
Options: (a) A aur R dono sahi, 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: Garam cold drink kholne par zyada jhaag nikalta hai. R: Taapmaan badhne par gases ki paani mein solubility ghat-ti hai.
✅ (a): garmi mein CO₂ kam ghul paati hai, isliye zyada gas bulbule bana kar nikalti hai. R seedha A ka kaaran hai.
2. A: Lakdi ka gutka paani mein tairta hai. R: Lakdi ka mass paani se kam hota hai.
✅ (c): A sahi hai. R galat hai, kyunki tairna mass se nahi, density se tay hota hai; bada latta bhaari hokar bhi tairta hai.
3. A: Clay ki goli ko chapta karne par uski density wahi rehti hai. R: Shape badalne se padarth ka mass aur volume nahi badalte.
✅ (a): mass aur volume wahi rehne se hi density wahi rehti hai; R, A ko samjhata hai.
📝 Very Short Answer (1 mark)
1. Solubility ki paribhasha do.
Kisi taapmaan par kisi solvent mein ghul sakne wali solute ki sabse zyada maatra.
2. Is chapter mein density ka kaun sa unit use hua?
g/cm³ (ya g/mL).
3. Hawa mein solvent ka kaam kaun si gas karti hai?
Nitrogen (lagbhag 78%, sabse zyada maatra mein).
4. 2.5 L ko mL mein badlo.
2500 mL.
5. Paani ki density lagbhag kitni hoti hai?
1 g/cm³.
🗒️ Short Answer (2–3 marks)
1. Saturated aur unsaturated solution mein do farq likho.
(1) Saturated mein us taapmaan par aur solute nahi ghulta; unsaturated mein ghul sakta hai. (2) Utne hi solvent mein saturated ghol mein sabse zyada solute hota hai, unsaturated mein usse kam.
2. Displacement method se ek chaabi ka volume kaise naapoge?
Measuring cylinder mein paani bhar kar level padho (jaise 30 mL). Chaabi ko dhaage se baandh kar poora duba do. Naya level padho (jaise 34 mL). Farq 34 − 30 = 4 mL = 4 cm³ chaabi ka volume hai.
3. Ek pathar ka mass 84 g aur volume 30 cm³ hai. Density nikaalo aur batao tairega ya doobega.
84 ÷ 30 = 2.8 g/cm³. 2.8 > 1, isliye doobega.
4. Garam paani thande paani ke upar kyun rehta hai?
Garam karne par paani phailta hai: mass wahi, volume zyada, toh density kam. Kam density wala garam paani zyada density wale thande paani ke upar aa jaata hai.
📄 Long Answer (5 marks)
1. Taapmaan ka (a) namak jaise solid ki aur (b) oxygen jaisi gas ki paani mein solubility par kya asar hota hai? Har ek ka ek roz ka udaaharan aur ek gadbad ka nateeja batao.
(a) Solid: taapmaan badhne par zyadatar solids ki solubility badhti hai. Udaaharan: chashni banaane ke liye cheeni garam paani mein ghuli jaati hai, thande mein utni nahi ghulti. Thandi saturated chashni garam karne par aur cheeni ghol leti hai.
(b) Gas: taapmaan badhne par gas ki solubility ghat-ti hai, kyunki garmi se gas ke kan tez bhaag kar bahar nikal jaate hain. Udaaharan: garam cold drink mein jaldi gas nikal jaati hai.
Nateeja: garmiyon mein ya factory ka garam paani nadi mein girne se paani mein oxygen kam ho jaati hai, aur machhliyon ko saans lene mein mushkil hoti hai.
2. Density kya hai? Iska formula aur unit likho. Ek cheez A (mass 200 g, volume 40 cm³) aur cheez B (mass 240 g, volume 60 cm³) ki tulna karo aur batao dono paani mein tairengi ya doobengi, kaaran ke saath.
Density: kisi padarth ke ek unit volume (1 cm³) ka mass. Formula: density = mass ÷ volume. Unit: g/cm³ ya g/mL (bade padarth ke liye kg/m³).
A: 200 ÷ 40 = 5 g/cm³. B: 240 ÷ 60 = 4 g/cm³. A zyada dense hai, jabki B ka mass zyada hai.
Dono ki density paani (1 g/cm³) se zyada hai, isliye dono doobengi. Isse saaf hai ki tairna ya doobna density se tay hota hai, sirf mass se nahi.
📰 Case-Based Question
(i) Namak neeche jamne lage, us samay ghol kaisa tha?
Saturated (us taapmaan par).
(ii) Garam karne par aur namak kyun ghula?
Garmi se namak (solid) ki solubility badhi, toh ghol phir se unsaturated ho gaya.
(iii) Aanda saade paani mein dooba par namak ke ghol mein tair gaya. Kyun?
Namak ghulne se ghol ka mass badha par volume lagbhag wahi raha, toh ghol ki density badh kar aande ki density se zyada ho gayi. Saade paani ki density aande se kam thi.
(iv) 1 litre paani kitne mL hai, aur is ghol mein solute aur solvent kaun hain?
1000 mL. Solute: namak; solvent: paani.
🚀 HOTS (Higher Order Thinking)
1. Ek steel ki plate doob jaati hai, par steel ka katora (bowl) tair jaata hai. Steel wahi hai, toh aisa kyun?
Steel ki density wahi hai. Par katore ke andar hawa bhari jagah hoti hai, toh “katora + andar ki hawa” ka kul volume bahut badh jaata hai aur ausat density paani se kam ho jaati hai. Plate mein yeh hawa wali jagah nahi, isliye woh doobti hai.
2. Ek saturated cheeni ka ghol fridge mein rakha. Kuch ghante baad bartan ke neeche cheeni ke daane dikhe. Samjhao.
Thande hone par cheeni ki solubility ghat gayi. Ab paani utni cheeni ghule hue nahi rakh sakta tha, toh extra cheeni daanon (crystals) ke roop mein bahar aa gayi.
3. Do bilkul ek jaise dikhne wale chamakdaar cube hain, dono 2 cm × 2 cm × 2 cm. Ek 63 g ka hai, doosra 21.6 g ka. Bina tode kaise bataoge ki dono alag dhaatu ke hain?
Volume = 2 × 2 × 2 = 8 cm³. Pehla: 63 ÷ 8 ≈ 7.9 g/cm³ (loha jaisa). Doosra: 21.6 ÷ 8 = 2.7 g/cm³ (aluminium jaisa). Density alag hai, toh padarth alag hain. Density padarth ki pehchaan hai.
🏆 Olympiad Corner
1. Ek khaali bartan ka mass 100 g hai. Use 50 mL ek liquid se bharne par kul mass 140 g ho jaata hai. Liquid ki density kya hai, aur woh paani mein tairega ya doobega (agar dono mile nahi)? (a) 2.8 g/mL, doobega (b) 0.8 g/mL, upar tairega (c) 1.25 g/mL, doobega (d) 0.4 g/mL, upar tairega
✅ (b): liquid ka mass = 140 − 100 = 40 g; density = 40 ÷ 50 = 0.8 g/mL < 1, upar rahega.
(a) bartan samet 140 g ko 50 se bhaag diya.
(c) ulta bhaag kiya (50 ÷ 40).
(d) 40 ÷ 100 kar diya, galat volume liya.
2. 20 °C par 100 g paani mein lagbhag 36 g namak ghulta hai. 250 g paani mein 20 °C par adhik se adhik kitna namak ghulega? (a) 36 g (b) 72 g (c) 90 g (d) 144 g
✅ (c) 90 g: 250 g = 2.5 × 100 g, toh 2.5 × 36 = 90 g.
(a) sirf 100 g paani ka jawaab.
(b) 200 g paani ka jawaab (2 × 36).
(d) 400 g paani ka jawaab (4 × 36).
3. Ek measuring cylinder mein 40 mL paani hai. Usme 10 ek jaisi kaanch ki goliyan daalne par level 55 mL ho gaya. Har goli ka mass 3.75 g hai. Ek goli ki density? (a) 1.5 g/cm³ (b) 2.5 g/cm³ (c) 0.4 g/cm³ (d) 37.5 g/cm³
✅ (b) 2.5 g/cm³: 10 goliyon ka volume = 55 − 40 = 15 cm³, ek ka 1.5 cm³; density = 3.75 ÷ 1.5 = 2.5.
(a) yeh ek goli ka volume hai, density nahi.
(c) ulta bhaag (1.5 ÷ 3.75).
(d) 10 goliyon ka kul mass (37.5 g) likh diya, volume se bhaag hi nahi diya.
Har option pe tap karo, turant pata chalega sahi ya galat.
Q1. 1.5 litre liquid ka mass 1800 gram hai. Density gram/cm³ mein?
(a) 1200 gram/cm³
❌ Galat: Litre ko cm³ mein nahi badla: 1800 ÷ 1.5 = 1200. 1500 cm³ lo: 1800 ÷ 1500 = 1.2.
(b) 0.83 gram/cm³
❌ Galat: Volume ÷ mass kiya: 1500 ÷ 1800 ≈ 0.83. Sahi: 1800 ÷ 1500 = 1.2.
(c) 300 gram/cm³
❌ Galat: Mass − volume kiya: 1800 − 1500 = 300. Density = 1800 ÷ 1500 = 1.2.
(d) 1.2 gram/cm³
✅ Sahi! Pehle unit: 1.5 litre matlab 1500 mL, yaani 1500 cm³. Density = 1800 ÷ 1500 = 1.2 gram/cm³.
Q2. Ek bucket mein 5 litre aata hai. Usme abhi 3200 mL water hai. Aur kitna water aayega?
(a) 1800 mL
✅ Sahi! 5 litre matlab 5 × 1000 = 5000 mL. Baaki = 5000 − 3200 = 1800 mL.
(b) 3195 mL
❌ Galat: Litre ko mL nahi banaya: 3200 − 5 = 3195. Pehle 5 litre = 5000 mL; 5000 − 3200 = 1800.
(c) 8200 mL
❌ Galat: Add kar diya: 5000 + 3200 = 8200. Baaki = 5000 − 3200 = 1800.
(d) 3200 mL
❌ Galat: Bhara hua water de diya (3200). Poocha baaki: 5000 − 3200 = 1800.
Q3. Pehla block: 60 gram, 20 cm³. Doosra block: 90 gram, 45 cm³. Kiski density zyada hai?
(a) Doosra block, kyunki mass zyada hai (90 gram)
❌ Galat: Heavy = dense maana. Har cm³ ka mass dekho: 60 ÷ 20 = 3, 90 ÷ 45 = 2.
(b) Pehla block: 3 gram/cm³ (doosra 2 gram/cm³)
✅ Sahi! Pehla: 60 ÷ 20 = 3. Doosra: 90 ÷ 45 = 2. 3 zyada hai.
(c) Doosra block, kyunki volume zyada hai (45 cm³)
❌ Galat: Bada volume = zyada density maana. Density: 3 vs 2, pehla zyada.
(d) Dono equal, kyunki dono solid hain
❌ Galat: Solid hone se density same maani. Calculate karo: 3 aur 2.
Q4. 20°C pe saturated sugar solution ko 60°C tak heat kiya. Ab woh kaisa hai?
(a) Saturated hi rahega
❌ Galat: Saturated ko har temperature pe same maana. Saturated hamesha ek temperature ke liye hota hai.
(b) Sugar crystals ban ke bahar aayegi
❌ Galat: Cooling ka result heating pe lagaya. Cool karne pe crystals bante hain, heat pe nahi.
(c) Unsaturated: ab aur sugar ghol sakta hai
✅ Sahi! Heat se sugar ki limit badhi. Pehle wali sugar limit se kam hai: unsaturated.
(d) Solution nahi raha, non-uniform ho gaya
❌ Galat: Heat ko non-uniform banana maana. Sugar ghuli hai: uniform solution hi hai.
Q5. Sea water ki density lagbhag 1.03 gram/cm³, plain water ki 1.00. Ek egg ki density 1.02 hai. Egg kahan float karega?
(a) Sirf plain water mein
❌ Galat: Compare reverse kar diya. Plain water (1.00) se egg (1.02) dense hai: sink.
(b) Dono mein
❌ Galat: Egg ko dono se light maana. Plain water mein 1.02 zyada hai 1.00 se: sink.
(c) Kisi mein nahi
❌ Galat: Egg ko dono se dense maana. Sea water 1.03 hai, egg 1.02: float.
(d) Sirf sea water mein: 1.02 sea water ke 1.03 se kam
✅ Sahi! Plain water: 1.02 zyada hai 1.00 se, to sink. Sea water: 1.02 kam hai 1.03 se, to float.
📚 Aur Padho (External Reference)
- NCERT Class 8 Science Curiosity, Chapter 9 (official PDF): chapter ke end mein “Keep the curiosity alive” wale poore sawaal aur chitra dekho
- DIKSHA: Sarkar ka free learning platform, NCERT ke videos ke liye
💖 CharuMam Motivation
Badhai ho! Aapne poora Chapter 9 khatam kar liya. 🎉 Yaad hai santra? Chhilka hata, toh woh doob gaya. Chhilke ne bas thodi si hawa pakad kar rakhi thi, aur wahi hawa use tairne ki taakat de rahi thi.
Hamari zindagi mein bhi aisa hi “chhilka” hota hai: umeed, achhe dost, aur roz ki thodi-thodi mehnat. Bahar se yeh halka lagta hai, par yahi humein mushkil ke paani mein doobne nahi deta. Aur yaad rakho, density shape se nahi badalti: aap kitne bhi thake ya chapte mehsoos karo, aapki asli taakat wahi rehti hai. Aaj chapter ke 12 sawaal bina dekhe kisi dost ko samjhao! 🌱
— CharuMam
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