MCQ practice · SSC Chemistry Board questions · Chapter 6: Concept of Mole and Chemical Counting
'X' is an element one atom of which has a mass of 3.985 × 10⁻²³ g. The relative atomic mass of 'X' is:
Think it through first, then pick an option.
- a 24
- b 12
- c 2.40
- d 0.024
Answer and explanation
Correct answer: a 24
3.985 × 10⁻²³ × 6.023 × 10²³ = 24 (Mg).
Why the other options are wrong
- b 12: 12 is half the answer; multiplying by the Avogadro number gives 24.
- c 2.40: 2.40 puts the decimal point in the wrong place; 3.985 × 6.023 ≈ 24.
- d 0.024: 0.024 mishandles the powers; 10⁻²³ × 10²³ = 1, so the answer is 24.
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