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Chapter 3 Atoms and Molecules NCERT Book Class 9 PDF (2026-27)
ATOMS AND MOLECULES
1. Which of the following correctly represents 360 g of water?
(i) 2 moles of H20
(ii) 20 moles of water
(iii) 6.022 × 1023 molecules of water
(iv) 1.2044×1025 molecules of water
(a) (i) (b) (i) and (iv)
(c) (ii) and (iii) (d) (ii) and (iv)
2. Which of the following statements is not true about an atom?
(a) Atoms are not able to exist independently
(b) Atoms are the basic units from which molecules and ions are formed
(c) Atoms are always neutral in nature
(d) Atoms aggregate in large numbers to form the matter that we can see, feel or touch
3. The chemical symbol for nitrogen gas is
(a) Ni (b) N2 (c) N+ (d) N
4. The chemical symbol for sodium is
(a) So (b) Sd (c) NA (d) Na
5. Which of the following would weigh the highest?
(a) 0.2 mole of sucrose (C12 H22 O11)
(b) 2 moles of CO2
(c) 2 moles of CaCO3
(d) 10 moles of H2O
6. What is the fraction of the mass of water due to neutrons?
7. Does the solubility of a substance change with temperature? Explain with the help of an example.
8. You are provided with a fine white coloured powder which is either sugar or salt. How would you identify it without tasting?
9. Calculate the number of moles of magnesium present in a magnesium ribbon weighing 12 g. Molar atomic mass of magnesium is 24g mol–1
10. The difference in the mass of 100 moles each of sodium atoms and sodium ions is 5.48002 g. Compute the mass of an electron.
11. Cinnabar (HgS) is a prominent ore of mercury. How many grams of mercury are present in 225 g of pure HgS? Molar mass of Hg and S are 200.6 g mol–1 and 32 g mol–1 respectively.
12. The mass of one steel screw is 4.11g. Find the mass of one mole of these steel screws. Compare this value with the mass of the Earth (5.98 × 1024kg). Which one of the two is heavier and by how many times?
13. A sample of vitamic C is known to contain 2.58 ×1024 oxygen atoms. How many moles of oxygen atoms are present in the sample?
14. Raunak took 5 moles of carbon atoms in a container and Krish also took 5 moles of sodium atoms in another container of same weight. (a) Whose container is heavier? (b) Whose container has more number of atoms?
15. Compute the number of ions present in 5.85 g of sodium chloride.
16. A gold sample contains 90% of gold and the rest copper. How many atoms of gold are present in one gram of this sample of gold?
17. What are ionic and molecular compounds? Give examples.
18. Compute the difference in masses of one mole each of aluminium atoms and one mole of its ions. (Mass of an electron is 9.1×10–28 g). Which one is heavier?
19. A silver ornament of mass ‘m’ gram is polished with gold equivalent to 1% of the mass of silver. Compute the ratio of the number of atoms of gold and silver in the ornament.
20. A sample of ethane (C2H6) gas has the same mass as 1.5 ×1020 molecules of methane (CH4). How manyC2H6 molecules does the sample of gas contain?
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