CBSE Class 9 Science Atoms and Molecules MCQs Set 04

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

Question. The chemical symbol for nitrogen gas is:
(a) \( \text{Ni} \)
(b) \( \text{N}_2 \)
(c) \( \text{Ne} \)
(d) \( \text{N} \)
Answer: (b) \( \text{N}_2 \)

Question. Which of the following correctly represents \( 360\text{ g} \) of water?
(i) \( 2 \) moles of water
(ii) \( 20 \) moles of water
(iii) \( 0.22 \times 10^{23} \) molecules of water
(iv) \( 12.044 \times 10^{25} \) molecules of water
(a) (i)
(b) (i) and (iv)
(c) (i) and (iii)
(d) (ii) and (iv)
Answer: (d) (ii) and (iv)

Question. Sanjana observed that when \( 3.0\text{ g} \) of carbon is burnt in \( 8.0\text{ g} \) of oxygen, \( 11.0\text{ g} \) of carbon dioxide is produced. Name the law of chemical combination will govern your answer?
(a) Law of definite proportions
(b) Law of conservation of energy
Answer: (a) Law of definite proportions

Question. Sanjana observed that when \( 3.0\text{ g} \) of carbon is burnt in \( 8.0\text{ g} \) of oxygen, \( 11.0\text{ g} \) of carbon dioxide is produced. Which postulate of Dalton's atomic theory is the result of law of conservation of mass?
(a) Atoms combine in the ratio of small whole numbers to form compounds.
(b) Atoms can neither be sub-divided, created nor destroyed
Answer: (b) Atoms can neither be sub-divided, created nor destroyed

Question. Assertion: Water molecules always contain hydrogen and oxygen in the ratio \( 1:8 \).
Reason: Water obeys law of constant proportions irrespective of source and method of preparation.
(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.
Answer: (a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).

Question. Assertion: Atoms can neither be sub-divided, created nor destroyed.
Reason: This postulate of Dalton's theory is the result of law of constant proportion
(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.
Answer: (c) Assertion (A) is true but reason (R) is false.

Question. Assertion: Carbonates are polyatomic ions.
Reason: The carbonate ion consists of one carbon atom and three oxygen atoms and carries an overall charge of \( -2 \).
(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.
Answer: (a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).

Question. Which of the following has maximum number of atoms?
(a) \( 18\text{ g} \) of water
(b) \( 18\text{ g} \) of carbon dioxide
(c) \( 18\text{ g} \) of ammonia
(d) \( 18\text{ g} \) of nitrogen
Answer: (d) \( 18\text{ g} \) of nitrogen

Question. Which of the following contains maximum number of molecules?
(a) \( 1\text{ g} \) of \( \text{CO}_2 \)
(b) \( 1\text{ g} \) of \( \text{N}_2 \)
(c) \( 1\text{ g} \) of \( \text{CH}_4 \)
(d) \( 1\text{ g} \) of \( \text{H}_2 \)
Answer: (c) \( 1\text{ g} \) of \( \text{CH}_4 \)

Question. Mass of one atom of oxygen is.
(a) \( 10\text{ g} \)
(b) \( 16\text{ g} \)
(c) \( 7\text{ g} \)
(d) \( 8\text{ u} \)
Answer: (b) \( 16\text{ g} \)

Question. \( 3.42\text{ g} \) of sucrose are dissolved in \( 18\text{ g} \) of water in a beaker. The number of oxygen atoms in the solution is:
(a) \( 6.68 \times 10^{23} \)
(b) \( 6.09 \times 10^{22} \)
(c) \( 6.022 \times 10^{23} \)
(d) \( 6.22 \times 10^{21} \)
Answer: (a) \( 6.68 \times 10^{23} \)

Question. 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

Question. How many atoms are there in Hydrogen chloride?
(a) \( 3 \)
(b) \( 4 \)
(c) \( 2 \)
(d) \( 6 \)
Answer: (c) \( 2 \)

Question. Assertion: Relative atomic mass of the atom of element is the average masses of the atom as compared to \( 1/12\text{-th} \) the mass of one carbon-12 atom.
Reason: Carbon-12 isotope is the standard reference for measuring atomic masses.
(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.
Answer: (c) Assertion (A) is true but reason (R) is false.

Question. Assertion: Atoms always combine to form molecules and ions.
Reason: Atoms of most elements are not able to exist independently.
(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.
Answer: (b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).

Question. Assertion: Atomicity of ozone is three while that of oxygen is two.
Reason: Atomicity is the number of atoms constituting a molecule.
(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.
Answer: (d) Assertion (A) is false but reason (R) is true.

ASSERTION REASONING QUESTIONS

Direction:
In each of the following questions, a statement of Assertion is given followed by a corresponding statement of Reason. Of the statements, mark the correct answer as
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true

Question. Assertion: The number of particles present in one mole of a substance is fixed.
Reason: The mass of one mole of a substance is equal to its relative atomic mass in gram
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true
Answer: (b) Both assertion and reason are true but reason is not the correct explanation of assertion.

Question. Assertion: Atoms always combine to form molecule and ions.
Reason: Atoms of most elements are not able to exist independently.
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true
Answer: (d) Assertion is false but reason is true

Question. Assertion: Atomicity of ozone is three while that of oxygen is two.
Reason: Atomicity is the number of atoms constituting a molecule.
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true
Answer: (a) Both assertion and reason are true and reason is the correct explanation of assertion.

Question. Assertion: On burning magnesium in oxygen, the mass of magnesium oxide formed is equal to the total mass of magnesium and oxygen
Reason: In a chemical substance, the elements are always present in a definite proportion.
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true
Answer: (b) Both assertion and reason are true but reason is not the correct explanation of assertion.

Question. Assertion: Molecular weight of oxygen is 16.
Reason: Atomic weight of oxygen is 16.
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true
Answer: (d) Assertion is false but reason is true

Question. Assertion: The number of moles of He in 52 g of He is 13.
Reason: The number of moles of an atom is the ratio of its given mass to its molar mass.
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true
Answer: (a) Both assertion and reason are true and reason is the correct explanation of assertion.

Question. Assertion: The chemical formula of aluminium oxide is \(\text{Al}_3\text{O}_2\)
Reason: The valency of aluminium is 3 and oxygen is 2.
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true
Answer: (d) Assertion is false but reason is true

Question. Assertion: A molecule is the smallest particle of an element or a compound which is capable of free existence.
Reason: The number of atoms present in one molecule of the substance is called its atomicity.
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true
Answer: (b) Both assertion and reason are true but reason is not the correct explanation of assertion.

Question. Assertion: Water molecules always contain hydrogen and oxygen in the ratio 1:8.
Reason: Water obeys law of constant proportions irrespective of source and method of preparation
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true
Answer: (a) Both assertion and reason are true and reason is the correct explanation of assertion.

Question. Assertion: Relative atomic mass of the atom of element is the average masses of the atom as compared to the mass of one carbon-12 atom.
Reason: Carbon-12 isotope is the standard reference for measuring atomic masses.
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true
Answer: (a) Both assertion and reason are true and reason is the correct explanation of assertion.

CASE BASED QUESTIONS

READ THE FOLLOWING PASSAGE AND ANSWER THE QUESTIONS

I. DALTON'S ATOMIC THEORY:

i) All matter is made of very tiny particles called atoms, which participate in chemical reactions. (ii) Atoms are indivisible particles, which cannot be created or destroyed in a chemical reaction. (iii) Atoms of a given element are identical in mass and chemical properties. (iv) Atoms of different elements have different masses and chemical properties. (v) Atoms combine in the ratio of small whole numbers to form compounds. (vi) The relative number and kinds of atoms are constant in a given compound.

Question. Which postulate of Dalton's atomic theory can explain law of definite proportions?
Answer: The relative number and kinds of atoms are constant in a given compound.

Question. Which all elements are present in the compound Calcium carbonate?
Answer: Ca, C, O

Question. Hydrogen and oxygen combine in the ratio of \( 1:8 \) by mass to form water. What mass of oxygen gas would be required to react completely with \( 3\text{ grams} \) of hydrogen gas?
Answer: \( 1\text{ g} \) of Hydrogen requires \( 8\text{g} \) of Oxygen. Therefore, \( 3\text{g} \) of Hydrogen will require \( 3 \times 8 = 24\text{g} \) of Oxygen

Question. Which postulate of Dalton specifies that the chemical formula of a compound will be the same always?
Answer: The relative number and kinds of atoms are constant in a given compound