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3. Atoms and Molecules-Additional -Questions 2 Science Class 9 In English
Last Updated : 06 March 2026
Explore science Solutions for Class 9 Chapter 3. Atoms and Molecules Topic Additional -Questions 2 in English medium.
3. Atoms and Molecules-Additional -Questions 2 Science Class 9 In English
Last Updated : 06 March 2026
3. Atoms and Molecules-Additional -Questions 2 Science Class 9 In English
3. Atoms and Molecules
Additional -Questions 2
Atoms and Molecules — Answers (Class 9)
उत्तर:
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सभी पदार्थ अति-सूক্ষ्म कणों (atoms) से बने होते हैं।
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किसी विशिष्ट तत्व के सभी atoms गुण (mass, properties) में समान होते हैं और अलग-अलग तत्वों के atoms अलग होते हैं।
उत्तर:
किसी molecule का molecular mass (मौलिक द्रव्यमान) = उस molecule में उपस्थित समस्त atoms के atomic masses का tổng (sum)। यह atomic mass units (u) में लिखा जाता है। उदाहरण: H₂O का molecular mass = 2×1 + 16 = 18 u.
उत्तर:
Avogadro संख्या = 6.022×10236.022\times 10^{23}6.022×1023. यह एक mole में उपस्थित कणों (atoms/molecules) की संख्या है।
उत्तर:
H₂O में कुल 3 atoms होते हैं — 2 hydrogen और 1 oxygen।
उत्तर:
यह नियम Joseph Proust ने दिया था। (Proust’s Law)
उत्तर:
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Molecule: एक साथ जुड़े हुए दो या अधिक atoms का समूह (same element के भी हो सकते हैं, जैसे O₂)।
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Compound: दो या अधिक विभिन्न तत्वों के atoms से बना पदार्थ जिसका निश्चित संरचना और गुण होते हैं (जैसे H₂O, NaCl)।
संक्षेप: हर compound molecule है पर हर molecule compound नहीं होता (यदि molecule में अलग-अलग तत्व न हों तो वह compound नहीं होगा)।
गणना:
CO₂ = 1×C + 2×O = 1×12+2×161\times 12 + 2\times 161×12+2×16.
=12+32=44= 12 + 32 = 44=12+32=44 u.
उत्तर: 44 u
गणना:
Water (H₂O) का molecular mass = 2×1+16=182\times1 + 16 = 182×1+16=18 g/mol.
Moles = mass / molar mass = 18 g÷18 g/mol=118\ \text{g} \div 18\ \text{g/mol} = 118 g÷18 g/mol=1 mol.
उत्तर: 1 mole
गणना:
Moles = 9 g÷18 g/mol=0.59\ \text{g} \div 18\ \text{g/mol} = 0.59 g÷18 g/mol=0.5 mol.
उत्तर: 0.5 mol
स्पष्टीकरण (mass-ratio method):
मान लीजिए कि magnesium और oxygen कुछ निश्चित mass ratio में मिलते हैं — वास्तविक atomic masses से दिखाएँ:
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Mg का atomic mass ≈ 24 (प्रायः 24.3)
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O का atomic mass = 16
यदि हम तुलना के लिए 24 g Mg और 16 g O लें:
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Mg के moles = 24÷24=124 \div 24 = 124÷24=1 mol
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O के moles = 16÷16=116 \div 16 = 116÷16=1 mol
mole का अनुपात = 1 : 1 → सबसे सरल whole-number ratio 1:1 → formula = MgO.
उत्तर: MgO
गणना/सिद्धि:
Water का वास्तविक mass-composition (H₂O): H का कुल mass = 2×1=22\times1 = 22×1=2 और O = 16 → H : O by mass = 2:16=1:82 : 16 = 1 : 82:16=1:8.
दिए गए उदाहरण में भी H : O = 2:16=1:82 : 16 = 1 : 82:16=1:8.
यह सुनिश्चित करता है कि किसी भी sample में H और O का mass-ratio स्थिर है — यही Law of Constant Proportion है।
उत्तर: हाँ, दिया हुआ मिश्रण उसी स्थिर अनुपात (1:8) में है, अतः नियम संतुष्ट होता है।
उत्तर (valency method):
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Na (sodium) की valency = 1 (यह 1+ ion देता है)।
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Cl (chlorine) की valency = 1 (यह 1– ion बनाता है)।
दोनों की valencies 1 और 1 हैं → एक-एक atom लेते हैं → formula = NaCl.
(वैकल्पिक mass-ratio से: Na और Cl के atomic masses से simplest whole number ratio भी 1:1 देगा।)
स्पष्टीकरण:
6.022×10236.022\times10^{23}6.022×1023 molecules = 1 mole (Avogadro संख्या)। CO₂ का molar mass हमने Q7 में निकाला = 44 g/mol.
इसलिए mass = 1 mol×44 g/mol=441\ \text{mol}\times 44\ \text{g/mol} = 441 mol×44 g/mol=44 g.
उत्तर: 44 g
गणना:
O₂ का molar mass = 2×16=322\times 16 = 322×16=32 g/mol.
Mass = moles × molar mass = 5×32=1605 \times 32 = 1605×32=160 g.
उत्तर: 160 g
स्पष्टीकरण:
1 mole किसी element का mass उसके atomic mass (g/mol) के बराबर होता है। यदि 1 mole = 32 g → atomic mass = 32 u (या 32 g/mol)।
उत्तर: 32 u (32 g/mol)
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