The correct answer is A because:

Calculate the number of moles for each option using moles = $\frac{mass}{relative molecular mass}$
- A: Relative molecular mass of ammonia = 14.0 + (3 x 1.0) = 17.0
  - n = $\frac{3.00}{17.0}$ = 0.18
- B: Relative molecular mass of chloromethane = 12.0 + (3 x 1.0) + 35.5 = 50.5
  - n = $\frac{3.00}{50.5}$ = 0.059
- C: Relative molecular mass of hydrogen sulfide = (2 x 1.0) + 32.1 = 34.1
  - n = $\frac{4.00}{34.1}$ = 0.12
- D: Relative molecular mass of hydrogen chloride = 1.0 + 35.5 = 36.5
  - n = $\frac{4.00}{36.5}$ = 0.11
Calculate the number of moles of atoms in each option:
- A: 0.18 x 4 = 0.75
- B: 0.059 x 5 = 0.30
- C: 0.12 x 3 = 0.36
- D: 0.11 x 2 = 0.22
Since option A contains the greatest number of moles of atoms, it will also contain the greatest number of atoms
- There is no need to use Avogadro's constant

B, C & D are incorrect as they do not contain the greatest number of (moles of) atoms

The Mole & the Avogadro Constant (CIE A Level Chemistry)

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