CBSE Class 9 Science Atoms and Molecules MCQs Set 05

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 grams.
(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. What is the law of conservation of mass?
(a) Mass can neither be created nor destroyed in a chemical reaction.
(b) Volume can neither be created nor destroyed in a chemical reaction.
(c) Mass can neither be created nor destroyed in a physical reaction.
(d) Mass can either be created nor destroyed in a physical reaction.
Answer: (a) Mass can neither be created nor destroyed in a chemical reaction.

Question. What is the law of constant proportions or law of definite proportions?
(a) In a chemical substance, the elements are not always present in a definite proportion by mass.
(b) In a chemical substance, the elements are always present in a definite proportion by mass.
(c) Mass can neither be created nor destroyed in a chemical reaction.
(d) Mass can neither be created nor destroyed in a physical reaction.
Answer: (b) In a chemical substance, the elements are always present in a definite proportion by mass.

Question. Which of the following is a non-metal that is tetra-atomic?
(a) Phosphorus.
(b) Helium
(c) Oxygen
(d) Hydrogen
Answer: (a) Phosphorus.

Question. Which is a triatomic molecule of elements?
(a) \( \text{S}_8 \)
(b) \( \text{O}_3 \)
(c) \( \text{H}_2 \)
(d) \( \text{He} \)
Answer: (b) \( \text{O}_3 \)

Question. Which is a polyatomic molecule of elements?
(a) \( \text{F} \)
(b) \( \text{Ar} \)
(c) \( \text{S}_8 \)
(d) \( \text{Ne} \)
Answer: (c) \( \text{S}_8 \)

Question. Name the anion that constitute the molecule of magnesium oxide.
(a) \( \text{Mg}^+ \)
(b) \( \text{O}^{-2} \)
(c) \( \text{Na} \)
(d) \( \text{Zn} \)
Answer: (b) \( \text{O}^{-2} \)

Question. Name the cation that constitute the molecule of magnesium oxide.
(a) \( \text{Mg}^{+2} \)
(b) \( \text{O}^{-2} \)
(c) \( \text{Na} \)
(d) \( \text{Zn} \)
Answer: (a) \( \text{Mg}^{+2} \)

Question. An element \( \text{X} \) has a valency \( 3 \). Write the formula of its oxide.
(a) \( \text{XO} \)
(b) \( \text{X}_2 \)
(c) \( \text{X}_2\text{O}_3 \)
(d) \( \text{XO}_3 \)
Answer: (c) \( \text{X}_2\text{O}_3 \)

Question. Which of the following compounds have polyatomic ions?
(a) \( \text{NaOH} \)
(b) \( \text{NaCl} \)
(c) \( \text{NaCl} \)
(d) \( \text{NaNO}_3 \)
Answer: (d) \( \text{NaNO}_3 \)

Question. Symbol of Iron
(a) \( \text{Fu} \)
(b) \( \text{Fe} \)
(c) \( \text{Ir} \)
(d) \( \text{In} \)
Answer: (b) \( \text{Fe} \)

Question. What is the atomicity of \( \text{CCl}_4 \) molecule?
(a) \( 1 \)
(b) \( 5 \)
(c) \( 7 \)
(d) \( 8 \)
Answer: (b) \( 5 \)

Question. What is the symbol of Lead?
(a) \( \text{Fl} \)
(b) \( \text{Pb} \)
(c) \( \text{Fe} \)
(d) \( \text{Fr} \)
Answer: (b) \( \text{Pb} \)

Question. What is the chemical formula of ammonium sulphate?
(a) \( (\text{NH}_4)_2\text{SO}_4 \)
(b) \( \text{H}_2\text{SO}_4 \)
(c) \( \text{CCl}_4 \)
(d) \( \text{NaCl} \)
Answer: (a) \( (\text{NH}_4)_2\text{SO}_4 \)

Question. An element 'X' forms an oxide with formula \( \text{X}_2\text{O}_3 \). State the valency of X.
(a) \( 3 \)
(b) \( 4 \)
(c) \( 5 \)
(d) \( 6 \)
Answer: (a) \( 3 \)

Question. What is the formula of ammonium chloride?
(a) \( \text{NH}_4\text{Cl} \)
(b) \( \text{H}_2\text{SO}_4 \)
(c) \( \text{CCl}_4 \)
(d) \( \text{NaCl} \)
Answer: (a) \( \text{NH}_4\text{Cl} \)

Question. What is the symbol of iron?
(a) \( \text{Fl} \)
(b) \( \text{Pb} \)
(c) \( \text{Fe} \)
(d) \( \text{Fr} \)
Answer: (c) \( \text{Fe} \)

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: Ions are always positively charged.
Reason: Ions are formed by losing or gaining of electrons.
(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: When 12 g of \(\text{CaCO}_3\) is decomposed, 4.6 g of residue is left and 4.4 g of escapes
Reason: Law of conservation of mass is not followed.
(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: Law of conservation of mass holds good for all the reactions.
Reason: It states that mass can neither be created nor destroyed in a chemical reaction.
(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: Atomicity of oxygen is 4.
Reason: 1 mole of an element contains \(6.023 \times 10^{23}\) atoms
(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: Atoms combine in fixed whole number ratio to form compounds
Reason: This postulate of Dalton’s theory is the result of law of constant 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: (a) Both assertion and reason are true and reason is the correct explanation of assertion.

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 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 total number of molecules present in 16 g of methane gas is \(60.22 \times 10^{23}\)
Reason: 1 mole of any substance contains \(6.023 \times 10^{23}\) atoms.
(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: All noble gases are monoatomic.
Reason: Noble gases are highly stable and unreactive.
(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: All atoms have a mass of 1u
Reason: Atoms of a given element are identical in mass and chemical properties.
(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: Symbol of aluminium is Al and not AL
Reason: The first letter of a symbol is always written as small letter (lowercase) and the second letter as a capital letter
(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: (c) Assertion is true but reason is false.

CASE BASED QUESTIONS

READ THE FOLLOWING PASSAGE AND ANSWER THE QUESTIONS

I. MOLECULE

A molecule is in general a group of two or more atoms that are chemically bonded together, that is, tightly held together by attractive forces. A molecule can be defined as the smallest particle of an element or a compound that is capable of an independent existence and shows all the properties of that substance. Atoms of the same element or of different elements can join together to form molecules. The number of atoms constituting a molecule is known as its atomicity.

Question. What is the atomicity of Phosphorous and \( \text{CCl}_4 \)?
Answer:
Phosphorous = 4
\( \text{CCl}_4 = 5 \)

Question. Classify the following as molecule of Element or compound:
a) \( \text{O}_2 \)
b) \( \text{CH}_4 \)
c) \( \text{NH}_3 \)
d) Ar
Answer:
a) \( \text{O}_2 \) = Element
b) \( \text{CH}_4 \) = compound
c) \( \text{NH}_3 \) = Compound
d) Ar - Element

Question. Why do atoms combine to form molecules?
Answer: Atoms are combining together to form molecules because they cannot exist independently but molecules are more stable and have independent existence.

Question. Which can exist freely H or \( \text{H}_2 \)?
Answer: \( \text{H}_2 \)