MCQ practice · SSC Chemistry Board questions · Chapter 6: Concept of Mole and Chemical Counting
How many molecules are in the H₂ gas used in the stimulus?
Think it through first, then pick an option.
- a 9.0345 × 10²³
- b 18.069 × 10²³
- c 9.0345 × 10²²
- d 18.069 × 10²²
Answer and explanation
Correct answer: a 9.0345 × 10²³
3 g H₂ = 3/2 = 1.5 mole; molecules = 1.5 × 6.023 × 10²³ = 9.0345 × 10²³.
Why the other options are wrong
- b 18.069 × 10²³: 18.069 × 10²³ is the number of H atoms, not molecules; the molecules number 9.0345 × 10²³.
- c 9.0345 × 10²²: The power is one short here; 1.5 mole of H₂ holds 9.0345 × 10²³ molecules.
- d 18.069 × 10²²: This is the atom count, with the power also off; the molecules number 9.0345 × 10²³.
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