$A$ hydrocarbon has $C = 85.72\%$ and the remaining is $H$. The hydrocarbon is:

By combustion of $0.2475 \ g$ of an organic compound,$0.4950 \ g$ of $CO_2$ and $0.2025 \ g$ of $H_2O$ are obtained. Calculate the percentage of $C, H,$ and $O$. Given atomic masses: $C = 12, H = 1, O = 16$.

$116 \ g$ of a substance upon dissociation reaction,yields $7.5 \ g$ of hydrogen,$60 \ g$ of oxygen and $48.5 \ g$ of carbon. Given that the atomic masses of $H, O$ and $C$ are $1, 16$ and $12$ respectively. The data agrees with how many formulae of the following?
$(A)$ $CH_3COOH$
$(B)$ $HCHO$
$(C)$ $CH_3OOCH_3$
$(D)$ $CH_3CHO$

$A$ compound $X$ contains $32 \%$ of $A$,$20 \%$ of $B$,and the remaining percentage of $C$. Then,the empirical formula of $X$ is:
(Given atomic masses of $A = 64$,$B = 40$,$C = 32 \ u$)

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

Calculate the mass of $Ca$ in $g$ present in $Ca(NO_3)_2$ that contains $20 \ g$ of nitrogen.