We are into the 3rd chapter of class 9 science NCERT textbook. Here we have chapter Atoms And Molecules. We have 30 MCQ questions for you with 10 MCQ from exemplar.
30 MCQ Questions for Class 9 Science: Chapter 3 Atoms And Molecules
Question 1. What is the formula unit mass of sodium chloride (NaCl)?
a) 23 u
b) 35.5 u
c) 58.5 u
d) 40 u
Answer:
c) 58.5 u
Question 2. The atomic mass of nitrogen is:
a) 12 u
b) 14 u
c) 16 u
d) 23 u
Answer:
b) 14 u
Question 3. What is the molecular mass of water (H₂O)?
a) 18 u
b) 17 u
c) 20 u
d) 22 u
Answer:
a) 18 u
Question 4. An ion with a positive charge is known as:
a) Anion
b) Cation
c) Neutron
d) Electron
Answer:
b) Cation
Question 5. Which law states that in a chemical reaction, the total mass of the reactants and products remains the same?
a) Law of Conservation of Mass
b) Law of Constant Proportions
c) Law of Multiple Proportions
d) Law of Definite Proportions
Answer:
a) Law of Conservation of Mass
Question 6. The smallest particle of an element that can participate in a chemical reaction is called:
a) Molecule
b) Atom
c) Ion
d) Compound
Answer:
b) Atom
Question 7. What kind of ion is formed when an atom loses an electron?
a) Negative ion
b) Positive ion
c) Neutral ion
d) Bipolar ion
Answer:
b) Positive ion
Question 8. The molecular mass of carbon dioxide (CO₂) is:
a) 44 u
b) 28 u
c) 32 u
d) 40 u
Answer:
a) 44 u
Question 9. Polyatomic ions are:
a) Ions made up of single atoms
b) Ions made up of multiple atoms
c) Ions made up of identical atoms
d) Neutral atoms
Answer:
b) Ions made up of multiple atoms
Question 10. The law of definite proportions was stated by:
a) John Dalton
b) Antoine Lavoisier
c) Joseph Proust
d) Dmitri Mendeleev
Answer:
c) Joseph Proust
Question 11. What is the valency of oxygen?
a) 1
b) 2
c) 3
d) 4
Answer:
b) 2
Question 12. What is the molecular mass of carbon dioxide (CO2)?
a) 44 u
b) 28 u
c) 32 u
d) 40 u
Answer:
a) 44 u
Question 13. The formula unit mass of NaCl (Sodium Chloride) is:
a) 23 u
b) 35.5 u
c) 58.5 u
d) 60.5 u
Answer:
c) 58.5 u
Question 14. Which of these is a polyatomic ion?
a) Na+
b) Cl-
c) NH4+
d) Mg2+
Answer:
c) NH4+
Question 15. The law of constant proportions was stated by:
a) John Dalton
b) Antoine Lavoisier
c) Joseph Proust
d) Dmitri Mendeleev
Answer:
c) Joseph Proust
Question 16. What is the atomicity of phosphorus in P4 molecules?
a) 2
b) 3
c) 4
d) 8
Answer:
c) 4
Question 17. What is the molar mass of sulphuric acid (H2SO4)?
a) 98 u
b) 100 u
c) 64 u
d) 82 u
Answer:
a) 98 u
Question 18. A molecule of ammonia (NH3) contains:
a) 1 nitrogen and 2 hydrogen atoms
b) 1 nitrogen and 3 hydrogen atoms
c) 2 nitrogen and 4 hydrogen atoms
d) 2 nitrogen and 3 hydrogen atoms
Answer:
b) 1 nitrogen and 3 hydrogen atoms
Question 19. What is the molecular formula of water?
a) H2O
b) HO
c) H2O2
d) HO2
Answer:
a) H2O
Question 20. The chemical formula of calcium carbonate is:
a) CaCO3
b) Ca2CO3
c) CaC2O4
d) Ca(CO3)2
Answer:
a) CaCO3
Question 21. The formula of sodium carbonate is __________.
Fill in the blank.
Answer:
Na2CO3
Question 22. Atoms of different elements having the same mass number but different atomic numbers are called __________.
Fill in the blank.
Answer:
Isobars
Question 23. The molar mass of oxygen molecule (O2) is __________ u.
Fill in the blank.
Answer:
32
Question 24. A group of atoms carrying a charge is known as a __________.
Fill in the blank.
Answer:
Polyatomic ion
Question 25. The molecular formula of ozone is __________.
Fill in the blank.
Answer:
O3
Question 26. A molecule of nitrogen (N2) contains two atoms. (True/False)
True / False
Answer:
True
Question 27. Atoms of isotopes have different physical properties but identical chemical properties. (True/False)
True / False
Answer:
True
Question 28. Compounds are substances composed of two or more types of elements. (True/False)
True / False
Answer:
True
Question 29. The atomic number of an element is equal to the number of protons in its nucleus. (True/False)
True / False
Answer:
True
Question 30. The mass of one mole of a substance is equal to its atomic mass expressed in grams. (True/False)
True / False
Answer:
True
Question on Match the Columns
Unmatched Columns – Questions
| Column A | Column B |
|---|---|
| (i) Dalton’s Atomic Theory | (a) Conservation of mass in reactions |
| (ii) Law of Conservation of Mass | (b) Indivisible nature of atoms |
| (iii) Law of Constant Proportions | (c) Atoms combine in simple whole number ratios |
| (iv) Molecular Mass | (d) Atoms of different elements have different masses |
| (v) Atomicity | (e) Same elements always combine in a fixed ratio by mass |
| (vi) Characteristics of Atoms | (f) Sum of atomic masses in a molecule |
Matched Columns – Answer
| Column A | Column B |
|---|---|
| (i) Dalton’s Atomic Theory | (b) Indivisible nature of atoms |
| (ii) Law of Conservation of Mass | (a) Conservation of mass in reactions |
| (iii) Law of Constant Proportions | (e) Same elements always combine in a fixed ratio by mass |
| (iv) Molecular Mass | (f) Sum of atomic masses in a molecule |
| (v) Atomicity | (c) Atoms combine in simple whole number ratios |
| (vi) Characteristics of Atoms | (d) Atoms of different elements have different masses |
MCQ questions from Exemplar Problems
Question 1. Which of the following correctly represents 360 g of water?
(i) 2 moles of H2O
(ii) 20 moles of water
(iii) 6.022 × 10^23 molecules of water
(iv) 1.2044 × 10^25 molecules of water
(a) (i)
(b) (i) and (iv)
(c) (ii) and (iii)
(d) (ii) and (iv)
Answer:
(d) (ii) and (iv) — 360 g ÷ 18 g/mol = 20 moles; molecules = 20 × 6.022 × 10^23 = 1.2044 × 10^25.
Question 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
Answer:
(a) Atoms are not able to exist independently — Some atoms (like noble gases) can exist independently.
Question 3. The chemical symbol for nitrogen gas is
(a) Ni
(b) N2
(c) N+
(d) N
Answer:
(b) N2 — Nitrogen gas is diatomic.
Question 4. The chemical symbol for sodium is
(a) So
(b) Sd
(c) NA
(d) Na
Answer:
(d) Na
Question 5. 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
Answer:
(c) 2 moles of CaCO3 — M(CaCO3)=100 g/mol, so 2 moles = 200 g (highest).
Question 6. Which of the following has maximum number of atoms?
(a) 18 g of H2O
(b) 18 g of O2
(c) 18 g of CO2
(d) 18 g of CH4
Answer:
(d) 18 g of CH4 — 18/16 = 1.125 moles of CH4; each molecule has 5 atoms → maximum atoms.
Question 7. Which of the following contains maximum number of molecules?
(a) 1 g CO2
(b) 1 g N2
(c) 1 g H2
(d) 1 g CH4
Answer:
(c) 1 g H2 — Smallest molar mass gives maximum moles (and hence molecules).
Question 8. Mass of one atom of oxygen is
(a) 16 / (6.023 × 10^23) g
(b) 32 / (6.023 × 10^23) g
(c) 1 / (6.023 × 10^23) g
(d) 8u
Answer:
(a) 16 / (6.023 × 10^23) g — One mole of O atoms (16 g) contains 6.023 × 10^23 atoms.
Question 9. 3.42 g of sucrose are dissolved in 18 g of water in a beaker. The number of oxygen atoms in the solution are
(a) 6.68 × 10^23
(b) 6.09 × 10^22
(c) 6.022 × 10^23
(d) 6.022 × 10^21
Answer:
(a) 6.68 × 10^23 — Water gives 6.022 × 10^23 O atoms; sucrose adds 0.11 × 6.022 × 10^23 ≈ 6.62 × 10^22; total ≈ 6.68 × 10^23.
Question 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 from the system
(c) when energy is either given to, or taken out from the system
(d) without any energy change
Answer:
(c) when energy is either given to, or taken out from the system — Heating or cooling can change state.
