## MCQ Questions for Class 9 Science: Ch 3 Atoms and Molecules

1. What is the value of Avogadroâ€™s number?
(a) 12.044 Ã— 1022
(b) 6.022 Ã— 1023
(c) 3.011 Ã— 1023
(d) 6.022 Ã— 1022
â–º

2. If 12 grams of carbon has n atoms, then the number of atoms in 12 grams of magnesium will be:
(a) 2n
(b) 3n
(c) n/2
(d) n
â–º (c) n/2

3. Which of the following is correct pair of elements and its symbol?
(a) Silver â€“ Si
(b) Sodium â€“ So
(c) Potassium â€“ Pt
(d) Sulphur â€“ S
â–º (d) Sulphur â€“ S

4. A student heats 25g of reactant â€˜Aâ€™ with 50g of reactant â€˜Bâ€™. He obtains 50g of product â€˜Câ€™ and recovers 25 g of unreacted â€˜Bâ€™. Which of the following law is confirmed in the following reaction?
(a) Law of constant proportion
(b) Law of conservation of mass
(c) Law of conservation of mass and Law of constant proportion
(d) Law of multiple proportion
â–º (c) Law of conservation of mass and Law of constant proportion

5. How many moles are present in 40 g of He?
(a) 10 moles
(b) 11 moles
(c) 13 moles
(d) 12 moles
â–º (a) 10 moles

6. Identify the symbol used to represent Avogadroâ€™s number.â€‹
(a) MA
(b) AO
(c) AN
(d) NA
â–º (d) NA

7. Law of conservation of mass can be derived from which postulate of Daltonâ€™s atomic theory?
(a) Atoms of a given element have same mass and chemical properties.
(b) Matter is made of tiny particles.
(c) Atom can neither be created nor destroyed.
(d) The relative number and kind of atoms are constant in a given compound.
â–º (c) Atom can neither be created nor destroyed.

8. Valency of hydrogen is 1 and that of sulphur is 2. What should be the formula of hydrogen sulphide?â€‹
(a) HS
(b) H2S2
(c) HS2
(d) H2S
â–º (d) H2S

9. Calculate the number of Mg atoms in 0.024 g of Mg
(a) 6.022 Ã— 1021 Mg atoms
(b) 6.22 Ã— 1023 Mg atoms
(c) 6.022 Ã— 1020 Mg atoms
(d) 6.022 Ã— 1025 Mg atoms
â–º (c) 6.022 Ã— 1020 Mg atoms

10. Which of the following is the major drawback of Daltonâ€™s atomic theory?
(a) Atoms of an element have exactly the same mass.
(b) Atoms are indivisible.
(c) Atoms of different elements have different masses.
(d) All of the above
â–º (b) Atoms are indivisible.

11. One atomic mass unit is a mass unit equal to exactly one twelfth (1/12th) the mass of one atom of ___________.
(a) Carbon-12
(b) Nitrogen -14
(c) Carbon-1
(d) Silicon-14
â–º (a) Carbon-12

12. If all the reactants in a chemical reaction are completely used, which of the following statements accurately describes the relationship between the reactants and the products?
(a) The reactants must contain more complex molecules than the products do.
(b) The products must have different physical state than the reactants.
(c) The total mass of the reactants must equal the total mass of the products.
(d) The density of the reactants must equal the density of the products.
â–º (c) The total mass of the reactants must equal the total mass of the products.

13. One mole of molecules may not be equal to:â€‹
(a) 6.022 x 1023 number of molecules
(b) Given number of particles (N)
(d) Molecular mass in grams
â–º (b) Given number of particles (N)

14. 9 grams of water decompose to give:
(a) 4g oxygen and 16g hydrogen
(b) 2g hydrogen and 1g oxygen
(c) 8g oxygen and 1g hydrogen
(d) none
â–º (c) 8g oxygen and 1g hydrogen

15. Who gave the Law of constant proportions?
(a) Cavendish
(b) Proust
(c) Dalton
(d) Lavoisier
â–º (b) Proust

16. According to Law of conservation of mass, mass of reactants wil be equal to the mass of:
(a) Catalysts
(b) Products
(c) Apparatus used for reaction
(d) Gases evolved
â–º (b) Products

17. How do atoms usually exist in nature?
(a) In the form of molecules
(b) In the form of ions
(c) In the free state
(d) In the form of molecules and Ions
â–º (d) In the form of molecules and Ions

18. What is the mass of 0.5 mole of Hydrogen atom
(a) 2.0 g
(b) 1.5 g
(c) 1 g
(d) 0.5 g
â–º (d) 0.5 g

19. The number of atoms present in one molecule of an element is called as:
(a) Empirical formula
(b) Molecule
(c) Atomicity
(d) Compound
â–º (c) Atomicity

20. Calculate the formula unit mass of ZnCl2?
(a) 137 u
(b) 124 u
(c) 123 u
(d) 111 u
â–º (a) 137 u

21. Which of the following pair of elements represents a mole ratio of 1:1?
(a) 20 g of sodium and 20 g of calcium
(b) 7 g of nitrogen and 12 gm of sodium
(c) 10 g of calcium and 6 g of carbon
(d) 14 g of nitrogen and 24 g of magnesium
â–º (d) 14 g of nitrogen and 24 g of magnesium

22. Which of the following is the correct IUPAC symbol for the element Cobalt?
(a) Co
(b) Cb
(c) C
(d) none of these
â–º (a) Co

23. Which of the following can be used to see atoms?
(a) Scanning tunneling microscope
(b) Microscope
(c) Most powerful microscope
(d) Optical microscope
â–º (a) Scanning tunneling microscope

24. Which one of the following is the modern symbol of Gold?
(a) Gl
(b) Go
(c) Si
(d) Au
â–º (d) Au

25. NaCl molecule is made of which of the following ions?
(a) Na cation and Cl anion
(b) Cl cation and Na anion
(c) Both Na and Cl cation
(d) Both Na and Cl anion
â–º (a) Na cation and Cl anion

26. An atom has a mass number of 23 and atomic number 11. The number of protons are ________.
(a) 11
(b) 12
(c) 23
(d) 44
â–º (a) 11

27. The balancing of chemical equation is based upon:
(a) Law of conservation of mass
(b) Law of multiple proportions
(c) Law of definite proportion
(d) Law of combining volumes
â–º (a) Law of conservation of mass

28. The number of moles of oxygen atoms in two moles of nitric acid is:
(a) 2
(b) 4
(c) 8
(d) 6
â–º (d) 6

29. During a chemical reaction, the sum of the masses of the reactants and products remains unchanged. This is known as
(a) Law of conservation of mass
(b) Law of multiple proportion
(c) Law of constant proportion
(d) None of these
â–º (a) Law of conservation of mass

30. Who was the first to use the symbols for elements?
(a) Joseph L Proust
(b) Berzillius
(c) Antoine L Lavoisier
(d) Dalton
â–º (d) Dalton

31. Valency of Calcium element is:
(a) 4
(b) 5
(c) 2
(d) 3
â–º (c) 2

32. The mass of 0.5 moles of Water molecules is:(Atomic mass, H =1; O = 16)
(a) 27 g
(b) 0.5 g
(c) 9 g
(d) 18 g
â–º (c) 9 g

33. Who stated the Law of conservation of mass?
(a) Thomson
(b) Lavoisier
(c) Dalton
(d) Cavendish
â–º (b) Lavoisier

34. Which constituent of air is monoatomic?
(a) Argon
(b) Water vapour
(c) Oxygen
(d) Nitrogen
â–º (a) Argon
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