$A$ compound contains $75.8\%$ of $X$ and $24.2\%$ of $Y$ by mass. If the atomic weights of $X$ and $Y$ are $24$ and $16$ respectively,find the empirical formula of the compound.

An organic compound has been found to possess the empirical formula $CH_2O$ and molecular weight $90$. The molecular formula of it is $(C = 12, H = 1, O = 16)$.

How much copper can be obtained from $100 \, g$ of copper sulphate $(CuSO_{4})$?

$20$ carat gold contains ...... $(\%)$ percent gold.

The molar mass of caffeine is $194$. It contains $28.9\%$ of nitrogen by mass. The number of nitrogen atoms in one molecule of caffeine is:

The complete combustion of $0.492 \, g$ of an organic compound containing $'C'$,$'H'$,and $'O'$ gives $0.793 \, g$ of $CO_{2}$ and $0.442 \, g$ of $H_{2}O$. The percentage of oxygen composition in the organic compound is .... (nearest integer)