$A$ substance contains $38.8\% \ C$,$16.0\% \ H$,and $45.2\% \ N$. What is the empirical formula of the substance?

An organic compound has an empirical formula of $CH_2O$ and a molecular mass of $90$. What is its molecular formula? $(C = 12, H = 1, O = 16)$

The molecular formula of sulphur is

In the crystalline solid $MSO_{4} \cdot nH_{2}O$ of molar mass $250 \ g \ mol^{-1}$, the percentage of anhydrous salt is $64$ by weight. The value of $n$ is

An oxygen-containing organic compound was found to contain $52 \%$ carbon and $13 \%$ hydrogen. Its vapour density is $23$. The compound reacts with sodium metal to liberate hydrogen. $A$ functional isomer of this compound is

Complete combustion of $X$ g of an organic compound gave $0.25$ g of $CO_2$ and $0.12$ g of $H_2O$. If the percentage of carbon is $25\%$ and of hydrogen is $4.89\%$, then $X = \_\_\_\_ \times 10^{-3}$ g. (Nearest integer) (Molar mass of $C$, $H$ and $O$ are $12, 1$ and $16$ g mol$^{-1}$ respectively.)