What is the percentage of nitrogen in urea (in $\%$)?

$925$ fine silver means an alloy of :

Empirical formula of a compound is $CH_2O$ and its vapour density is $30$. The molecular formula of the compound is:

The percentage of $Se$ in peroxidase anhydrous enzyme is $0.5\%$ by weight (atomic weight $= 78.4$). Then,the minimum molecular weight of peroxidase anhydrous enzyme is:

Compound $A$ contains $8.7\,\%$ Hydrogen,$74\,\%$ Carbon and $17.3\,\%$ Nitrogen. The molecular formula of the compound is ....
Given : Atomic masses of $C$,$H$ and $N$ are $12$,$1$ and $14\, amu$ respectively.
The molar mass of the compound $A$ is $162\, g\, mol^{-1}$.

In an $80 \, g$ compound,the masses of elements are $C = 24 \, g$,$H = 4 \, g$,and $O = 32 \, g$. Find its empirical formula.