What is the mass percent of oxygen in ethanol $(C_2H_5OH)$ (in $\%$)?

$A$ certain compound has the molecular formula $X_4O_6$. If $10 \ g$ of $X_4O_6$ has $5.72 \ g$ of $X$,the atomic mass of $X$ is ............ $amu$.

Substances $X$ and $Y$ have the same mass. If their atomic weights are $30$ and $20$ respectively,and the molecular weight of the compound is $120$,what is the molecular formula of the compound?

The percentage of $P_2O_5$ in diammonium hydrogen phosphate $(NH_4)_2HPO_4$ is

$A$ compound gave $80\%$ carbon and $20\%$ hydrogen on analysis. The compound is possibly

Define Percentage Composition in a compound.