Calculate the mass percent of different elements present in sodium sulphate $(Na_{2}SO_{4})$.

The molecular formula of sodium sulphate is $Na_{2}SO_{4}$.
Molar mass of $Na_{2}SO_{4} = [(2 \times 23.0) + (32.066) + 4(16.00)] = 142.066 \ g/mol$.
Mass percent of an element $= \frac{\text{Mass of that element in the compound}}{\text{Molar mass of the compound}} \times 100$.
Mass percent of sodium $= \frac{46.0}{142.066} \times 100 = 32.379 \% \approx 32.4 \%$.
Mass percent of sulphur $= \frac{32.066}{142.066} \times 100 = 22.571 \% \approx 22.6 \%$.
Mass percent of oxygen $= \frac{64.0}{142.066} \times 100 = 45.049 \% \approx 45.05 \%$.