$A$ substance contains $38.8\%$ carbon,$16\%$ hydrogen,and $45.2\%$ nitrogen. What is the empirical formula of this substance?

Calculate the percentage composition of element $P$ in ${H_3PO_4}$. (in $\%$)

How much copper can be obtained from $100 \ g$ of copper sulfate $(CuSO_4)$ (in $g$)?

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.)

An alkane has a $C/H$ ratio (by mass) of $5.1428$. Its molecular formula is

An organic compound on analysis gave the following results: $C = 54.5\%$,$O = 36.4\%$,$H = 9.1\%$. The empirical formula of the compound is: