CBSE Class 9 Science Atoms and Molecules Worksheet Set A

Question. 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.
Answer : C

Question. 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
Answer : C

Question.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.
Answer : C

Question. 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
Answer : B

Question. 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

Question. Match List-I with List-II and mark the correct option.
              List-I                          List-II
(P) 0.25 mole oxygen      1. 6.022 × 1023 molecules
(Q) 18 g water                 2. 1.505 × 1023 molecules
(R) 46 g Na atom            3. 6.022 × 1023 atoms
(S) 1 mole C atom           4. 12.044 × 1023 atoms
(a) P-1, Q-2, R-3, S-4
(b) P-2, Q-1, R-4, S-3
(c) P-4, Q-1, R-3, S-2
(d) P-1, Q-4, R-3, S-2
Answer : B

Question. 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
Answer : A

Question. The mass of a molecule of water is
(a) 3 × 10^–26 kg
(b) 3 × 10^–25 kg
(c) 1.5 × 10^–26 kg
(d) 2.5 × 10^–26 kg
Answer : A

Question. 52 g of He contains
(a) 4 × 6.022 × 10²³ atoms
(b) 13 atoms
(c) 13 × 6.022 × 10²³ atoms
(d) 4 atoms
Answer : C

Question. How many grams of H₂SO₄ are present in 0.25 mole of H₂SO₄?
(a) 2.45
(b) 24.5
(c) 0.245
(d) 25.4
Answer : B

Question. 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
Answer : C

Question. 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.
Answer : A

Question. How many atoms in total are present in CoCl₃.6H₂O?
(a) 17
(b) 22
(c) 8
(d) 18
Answer : B

Question. Match the columns by choosing the correct option.
   Column I              Column II
(A) 52 g of He          (i) 2 moles
(B) 8 g of O₂            (ii) 1 mole
(C) 2 g of H₂            (iii) 0.25 mole
(D) 56 g of N₂          (iv) 13 moles
(a) (A)-(i), (B)-(iv), (C)-(iii), (D)-(ii)
(b) (A)-(iii), (B)-(ii), (C)-(i), (D)-(iv)
(c) (A)-(iv), (B)-(iii), (C)-(ii), (D)-(i)
(d) (A)-(iii), (B)-(i), (C)-(iv), (D)-(ii)
Answer : C

Question. 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
Answer : B

Question. 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
Answer : C

Question. Which of the following molecules are diatomic?
(i) Nitrogen (ii) Neon (iii) Oxygen
(iv) Sulphur (v) Phosphorus (vi) Ozone
(vii) Fluorine (viii)Hydrogen (ix) Fullerene
(a) (ii), (iv), (v) and (vi)
(b) (iv), (v) and (ix)
(c) (ii) and (vi)
(d) (i), (iii), (vii) and (viii)
Answer : D

Question. 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
Answer : B

Question. 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

Question. Match the columns by choosing the correct option.
Column I                              Column II
(Molecule)                       (Mass ratio of elements)
(A) Water (H : O)                      (i) 14 : 3
(B) Ammonia (N : H)                 (ii) 1 : 8
(C) Carbon dioxide (C : O)         (iii) 1 : 1
(D) Sulphur dioxide (S : O)        (iv) 3 : 8
(a) (A) - (ii), (B) - (i), (C) - (iv), (D) - (iii)
(b) (A) - (iii), (B) - (ii), (C) - (i), (D) - (iv)
(c) (A) - (i), (B) - (iv), (C) - (iii), (D) - (ii)
(d) (A) - (iv), (B) - (iii), (C) - (ii), (D) - (i)
Answer : A

Question. Arrange the following in the order of increasing mass. (Atomic mass of O = 16 u,Cu = 63 u, N = 14 u)
I. one atom of oxygen
II. one atom of nitrogen
III. 1 × 10–10 mole of oxygen gas
IV. 1 × 10–10 mole of copper
(a) II < I < III < IV
(b) I < II < III < IV
(c) III < II < IV < I
(d) IV < II < III < I
Answer : A

Question. 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
Answer : C

Question. The formula of chloride of a metal M is MCl₃,then the formula of the phosphate of metal M will be
(a) MPO₄
(b) M₂PO₄
(c) M₃PO₄
(d) M₂(PO₄)₃
Answer : A

Question. Which of the following has highest number of molecules?
(a) 8 g of CH₄
(b) 4.4 g of CO₂
(c) 34.2 g of C₁₂H₂₂O₁₁
(d) 2 g of H₂
Answer : A

Question. 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.
Answer : B

Question. 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.
Answer : B

Question. 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
Answer : D

Question. Which of the following correctly represents 360 g of water?
(i) 2 moles of H₂O
(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)
Answer : D

Question. 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)
Answer : C

Question. 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 × 10²³
(b) 6.09 × 10²²
(c) 6.022 × 10²³
(d) 6.022 × 10²¹
Answer : A

Question. It was found that 0.10 mole of MSO₄ combines with 9.0 g of water to form the hydrate salt MSO₄.nH₂O. What is the value of n?
(a) 2
(b) 3
(c) 4
(d) 5
Answer : D

Question. The molecular mass of X is 106. X among the following is
(a) CaCO₃
(b) SO₃
(c) Na₂CO₃
(d) NaCl
Answer : C