MCQ Questions for Class 9 Science Chapter 3 Atoms and Molecules

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MCQ Questions for Class 9 Science Chapter 3 Atoms and Molecules help to identify the areas where the students need more work. They play a very significant role in your final preparation for the exams.

The questions are also helpful for the students who want to improve their time management skills. Chapter 3 Class 9 Science CBSE MCQ Questions with answers are helpful for helping students understand the material they are studying.

Chapter 3 Atoms and Molecules Class 9 Science MCQ Questions

1. Which one of the following pair of gases contains the same number of moles?
(a) 16 g of O2 and 14 g of N2
(b) 8 g of O2 and 22 g of CO2
(c) 28 g of N2 and 22 g of CO2
(d) 32 g of O2 and 32 g of N2
▶ (a) 16 g of O2 and 14 g of N2

2. What mass of carbon dioxide (CO2) will contain 3.011 1023 molecules?
(a) 11.0 g
(b) 22.0 g
(c) 4.4 g
(d) 44.0 g
▶ (b) 22.0 g

3. All samples of carbon dioxide contain carbon and oxygen in the mass ratio 3:8. This is in agreement with the law of
(a) conservation of mass
(b) constant proportions
(c) multiple proportions
(d) gaseous volumes
▶ (b) constant proportions

4. A sample of pure water, irrespective of its source contains 11.1% hydrogen and 88.9% oxygen. The data supports
(a) law of constant proportions
(b) law of conservation of mass
(c) law of reciprocal proportions
(d) law of multiple proportions
▶ (a) law of constant proportions

5. How many grams of H2SO4 are present in 0.25 mole of H2SO4?
(a) 2.45
(b) 24.5
(c) 0.245
(d) 0.25
▶ (b) 24.5

6. Elements belonging to different groups of the periodic table are given below. If the element X forms a chloride whose formula is ‘XCl2‘ then element ‘X’ belongs to the group whose representative element is
(a) Al
(b) Na
(c) Mg
(d) Si
▶ (c) Mg

7. 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.
▶ (a) Atoms are not able to exist independently.

8. The number of atoms present in a molecules of a substance is called
(a) molecularity
(b) atomicity
(c) valency
(d) reactivity
▶ (b) atomicity

9. If 12 g of carbon burns completely in 40 g oxygen in a closed container, the product has
(a) 44 g of carbon dioxide
(b) 8 g of oxygen
(c) both (a) and (b)
(d) none of these
▶ (c) both (a) and (b)

10. The number of atoms in 0.1 mole of a triatomic gas is
(a) 6.026 × 1022
(b) 1.806 × 1023
(c) 3.6 × 1023
(d) 1.8 × 1022
▶ (b) 1.806 × 1023

11. Identify the incorrect statement.
(a) The building blocks of all matter are atoms.
(b) Atoms are very small. They cannot be seen by the naked eye.
(c) The size of an atom is expressed in metres.
(d) An atom of hydrogen has the radius of the order of 10-10 m.
▶ (c) The size of an atom is expressed in metres.

12. A sample of pure water, irrespective of its source contains 11.1% hydrogen and 88.9% oxygen. The data supports
(a) law of constant proportions
(b) law of conservation of mass
(c) law of reciprocal proportions
(d) law of multiple proportions
▶ (a) law of constant proportions

13. Molecular mass is defined as the
(a) mass of one atom compared with the mass of one molecule
(b) mass of one atom compared with the mass of one atom of hydrogen
(c) mass of one molecule of any substance compared with the mass of one atom of C-12
(d) none of the above
▶ (c) mass of one molecule of any substance compared with the mass of one atom of C-12

14. An atom is the
(a) smallest particle of matter known
(b) smallest particle of a gas
(c) smallest particle of an element that can take part in a chemical change
(d) radioactive emission
▶ (c) smallest particle of an element that can take part in a chemical change

15. Valency of silver in Ag2S is
(a) 1
(b) 2
(c) 0
(d) 3
▶ (a) 1

16. A chemical equation is always balanced to fulfil the condition of
(a) Dalton’s atomic theory
(b) law of constant composition
(c) law of multiple proportions
(d) law of conservation of mass
▶ (d) law of conservation of mass

17. Identify the correct statements.
(i) In a compound such as water, the ratio of the mass of hydrogen to the mass of oxygen is always 8 1.
(ii) If 9 g of water is decomposed, 1 g of hydrogen and 8 g of oxygen are always obtained.
(iii) In ammonia, nitrogen and hydrogen are always present in the ratio 3 : 14 by mass.
(iv) Many compounds are composed of two or more elements and each such compound has the same elements in the same proportions.
(a) (i) and (iii)
(b) (i), (ii) and (iii)
(c) (ii) and (iv)
(d) All of these
▶ (c) (ii) and (iv)

18. Which of the following pair of elements represents a mole ratio of 1: 1?
(a) 10 g of calcium and 12 g of magnesium
(b) 12 g of magnesium and 6 g of carbon
(c) 12 g of carbon and 20 g of calcium
(d) 20 g of sodium and 20 g of calcium
▶ (b) 12 g of magnesium and 6 g of carbon

19. Latin name for gold is
(a) aurum
(b) kalium
(c) natrium
(d) ferrum
▶ (a) aurum

20. In which of the following the valency of each of the constituent elements is equal to the total number of atoms is one molecule of the compound?
(a) HCl
(b) H2S
(c) CaO
(d) MgCl2
▶ (c) CaO

21. Which of the following has the smallest mass?
(a) 4 g of He
(b) 6.022 × 1023 atoms of He
(c) 1 atom of He
(d) 1 mole atoms of He
▶ (c) 1 atom of He

22. If three gases X, Y and Z are arranged in increasing order of their relative molecular mass and the mass of each gas is 10 g at S.T.P state, which gas will contain the least number of molecules and which will contain the most?
(a) X least and Y maximum
(b) X maximum and Z least
(c) Y maximum and Z least
(d) Y least and Z maximum
▶ (b) X maximum and Z least

23. All samples of carbon dioxide contain carbon and oxygen in the mass ratio 3 : 8. This is in agreement with the law of
(a) conservation of mass
(b) constant proportions
(c) multiple proportions
(d) gaseous volumes
▶ (b) constant proportions

24. Which of the following would weigh the highest?
(a) 0.2 mole of sucrose (C12H22O11)
(b) 2 moles of CO2
(c) 2 moles of CaCO3
(d) 10 moles of H2O
▶ (b) 2 moles of CO2

25. The total number of electrons present in 16 g of methane gas is
(a) 96.352 × 1023
(b) 48.176 × 1023
(c) 60.22 × 1023
(d) 30.110 × 1023
▶ (c) 60.22 × 1023

26. Two gaseous samples were analysed. One contained 1.2 g of carbon and 3.2 g of oxygen. The other contained 27.3% carbon and 72.7% oxygen. The experimental data are in accordance with
(a) law of conservation of mass
(b) law of definite proportions
(c) law of reciprocal proportions
(d) law of multiple proportions
▶ (b) law of definite proportions

27. Arrange the following in the increasing order of mass in grams:
(i) One atom of silver
(ii) Two grams atom of nitrogen
(iii) One mole of calcium
(iv) Two grams of sodium
[At. masses : Ag = 108 u, N = 14 u, Ca = 40 u, Na = 23 u]
(a) (i) < (ii) < (iii) < (iv)
(b) (iv) < (iii) < (ii) < (i)
(c) (i) < (iv) < (ii) < (iii)
(d) (iii) < (ii) < (i) < (iv)
▶ (c) (i) < (iv) < (ii) < (iii)

28. Which of the following weighs most?
(a) 2 g atoms of nitrogen
(b) 25 g iron
(c) 2 × 1023 atoms of carbon
(d) 1 mole of SO2
▶ (d) 1 mole of SO2

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