Molecular and Formula Mass MCQs

Q1. One mole of any substance contains how many particles?

• A.6.022 x 10^23 (Avogadro's number)
• B.1000
• C.6.022 x 10^-23
• D.12

Answer: A. 6.022 x 10^23 (Avogadro's number)

NCERT fact (chemistry, chapter 'Atomic Foundations of Matter'): Number of moles n = given mass / molar mass; compute the molar mass by summing atomic masses, then n = m / M => substituting the data yields the quoted result; hence the answer = 6.022 x 10^23 (Avogadro's number). Why option A fits - Correct. Distractor analysis: option B) '1000' is incorrect: A mole is 6.022 x 10^23 particles, not 1000; option C) '6.022 x 10^-23' is incorrect: Avogadro's number is 6.022 x 10^23, a large number (positive exponent). Final answer - A) 6.022 x 10^23 (Avogadro's number).

Q2. Why do we use 'formula unit mass' for NaCl instead of 'molecular mass'?

• A.NaCl exists as a giant ionic lattice, not separate molecules
• B.NaCl is a gas of separate molecules
• C.NaCl has no mass
• D.sodium and chlorine are not elements

Answer: A. NaCl exists as a giant ionic lattice, not separate molecules

Q3. The molecular mass of a substance is the:

• A.sum of the atomic masses of all atoms in one molecule
• B.mass of one atom only
• C.number of molecules in a sample
• D.mass of the container

Answer: A. sum of the atomic masses of all atoms in one molecule