Atoms and Molecules Class 9 Questions (MCQs)

Atoms and Molecules Class 9 Questions

Que 1. Which of the following correctly represents 360 g of water?
(i) 2 moles of water
(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)

Que 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.

Que 3. 1 u or 1 amu means
(a) 1/12th mass of C-12 atoms
(b) Mass of C-12 atom
(c) Mass of O-16 atom
(d) Mass of Hydrogen molecule

Que 4. Which of the following contains the maximum number of molecules?
(a) 19 CO₂
(b) 1g N₂
(c) 1g H₂
(d) 1g CH₄

Que 5. A sample of NH₃ molecule irrespective of source contains 82.35% Nitrogen and 17.65%  Hydrogen by mass. This data supports:
(a) Law of Conservation of Mass
(b) Las of Multiple Proportions
(c) Law of Definite Proportions
(d) Avogadro’s Law

Que 6. An element X is divalent and another element Y is tetravalent. The compound formed by these two elements will be:
(a) XY
(b) XY₂
(c) X₂Y
(d) XY₄

Que 7. The molecular formula of potassium nitrate is.
(a) KNO₃
(b) KNO
(c) KNO₂
(d) KON

Que 8. 3.42 g of sucrose are dissolved in 18 g of water in a beaker. The numbers of oxygen atoms in the solution are:
(a) 6.68 × 10²³
(b) 6.09 × 10²²
(c) 6.022 × 10²³
(d) 6.022 × 10²¹

Que 9. Molecular mass is defined as the:
(a) Mass of one molecule of any substance compared with the mass of one atom of C–12
(b) Mass of one atom compared with the mass of one atom of hydrogen
(c) Mass of one atom compared with the mass of one molecule
(d) None of the above

Que 10. A change in the physical state can be brought about
(a) only when energy is given to the system
(b) only when energy is taken out of the system
(c) When energy is either given to or taken out from the system
(d) Without any energy change

Atoms and Molecules Class 9 Questions

Que 11. The atomic mass of sodium is 23. The number of moles in 46g of sodium is —–.
(a) 4
(b) 2
(c) 0
(d) ½

Que 12. Which of the following represents a correct chemical formula?
(a) CaCl
(b) BiPO₄
(c) NaSO₄
(d) NaS

Que 13. What is the formula mass unit of ZnO?
(a) 18 u
(b) 81 u
(c) 88 u
(d) 188 u

Que 14. How many atoms of oxygen are present in 300 grams of CaCO₃?
(a) 54.207 × 10²³
(b) 6.207 × 10²³
(c) 12.207 × 10²³
(d) 22.2 × 10²³

Que 15. Which of the following represents the correct relation between Avogadro’s number (N_o), number of particles (N), and moles (n)?
(a) n = N / No
(b) n = No / N
(c) n = N No
(d) all are correct

Atoms and Molecules Class 9 Questions

Assertion Reason type Questions:

Two statements are given- one labeled Assertion (A) and the other labeled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:
(a) Both Assertion and Reason are correct, and reason is the correct explanation for assertion.
(b) Both Assertion and Reason are correct, and Reason is not the correct explanation for Assertion.
(c) Assertion is true but Reason is false.
(d) Both Assertion and Reason are false.

Que 16. Assertion: The atom is the smallest unit of a molecule
Reason: Atom is not seen by our naked eyes.

Que 17. Assertion: The atom is the smallest unit of the molecule
Reason: Atoms are combined with each other forming molecules.
 

Answers:

Ans 1. (d) (ii) and (iv)

Ans 2. (d) Atoms aggregate in large numbers to form the matter that we can see, feel, or touch.

Ans 3. (a) 1/12th mass of C-12 atoms

Ans 4. (c) 1g H₂

Ans 5. (c) Law of Definite Proportions

Ans 6. (b) XY₂

Ans 7. (a) KNO₃

Ans 8. (a) 6.68 × 10²³

Ans 9. (a) Mass of one molecule of any substance compared with the mass of one atom of C–12

Ans 10. (c) When energy is either given to, or taken out from the system

Ans 11. (b) 2

Ans 12. (b) BiPO₄

Ans 13. (b) 81 u

Ans 14. (a) 54.207 × 10²³

Ans 15. (a) n = N / N_o

Ans 16. (b) Both Assertion and Reason are correct, and Reason is not the correct explanation for Assertion.

Ans 17. (b) Both Assertion and Reason are correct, and Reason is not the correct explanation for Assertion.

Atoms and Molecules Class 9 Questions