Which contains more molecules, 10 g of sulphur dioxide (SO₂) or 10 g of oxygen (O₂) ?
(Atomic masses : S = 32 u ; O = 16 u)

Given:
Mass of sulphur dioxide = 10g
Molar mass of sulphur dioxide = (1 × 32) + (2 × 16) = 64g
We know that 64g of sulphur dioxide contain 6.022 × 10²³ molecules.
Number of molecules in 64g sulphur dioxide = 6.022 × 10²³
Number of molecules in 10g sulphur dioxide = 10 × 6.022 × 10²³/ 64
Hence, the number of molecules in 10g sulphur dioxide is 9.4× 10²².
Given:
Mass of oxygen = 10g
Molar mass of oxygen molecule = (2 × 16) = 32g
Number of molecules in 32g oxygen = 6.022 × 10²³
Number of molecules in 10g oxygen = 10 × 6.022 × 10²³/ 32
Hence, the number of molecules in 10g oxygen is 18.8 × 10²²
It is clear that the number of atoms in 10g oxygen is greater than that in 10g sulphur dioxide.