$A$ substance contains $38.8\% \, C$,$16\% \, H$,and $45.2\% \, N$. What is the empirical formula of the substance?

The percentage composition of carbon by mole in methane is ........... $ \% $

The empirical formula of a compound is $CH_2O$. If its molecular weight is $180$,what is the molecular formula of the compound?

An organic compound contains $A$ and $B$ in a mass ratio of $50:50$. If their atomic masses are $10$ and $40$ respectively,then its empirical formula will be ....................

$A$ $64 \, g$ organic compound contains $24 \, g$ of carbon,$8 \, g$ of hydrogen,and the rest is oxygen. The empirical formula of this compound is .....

The empirical formula of a compound is $CH_2O$ and its vapor density is $30$. The molecular formula of the compound is ......