Define Percentage Composition in a compound.

Percentage composition of a compound is the mass percentage of each element present in it. It helps in determining the purity of a given sample.
The formula for calculating the mass percentage of an element is:
$\text{Mass } \% \text{ of an element} = \frac{\text{mass of that element in the compound} \times 100}{\text{molar mass of the compound}}$
For example,in water $(H_2O)$:
Molar mass of water $= 18.02 \ g/mol$
$\text{Mass } \% \text{ of hydrogen} = \frac{2 \times 1.008}{18.02} \times 100 = 11.18 \%$
$\text{Mass } \% \text{ of oxygen} = \frac{16.00}{18.02} \times 100 = 88.79 \%$
Similarly,for ethanol $(C_2H_5OH)$ with molar mass $46.068 \ g/mol$:
$\text{Mass } \% \text{ of carbon} = \frac{24.02}{46.068} \times 100 = 52.14 \%$
$\text{Mass } \% \text{ of hydrogen} = \frac{6.048}{46.068} \times 100 = 13.13 \%$
$\text{Mass } \% \text{ of oxygen} = \frac{16.00}{46.068} \times 100 = 34.73 \%$