The empirical formula of a compound is $CH_2$. If the molar mass of the compound is $42 \ g/mol$,what is its molecular formula?

On complete combustion of $0.492 \ g$ of an organic compound containing $C, H$ and $O$,$0.7938 \ g$ of $CO_2$ and $0.4428 \ g$ of $H_2O$ were produced. The percentage composition of oxygen in the compound is $........$

$0.5 \ g$ of an organic compound on combustion gave $1.46 \ g$ of $CO_2$ and $0.9 \ g$ of $H_2O$. The percentage of carbon in the compound is $...........$ ($NEAREST$ $INTEGER$). [$GIVEN$: Molar mass in $g \ mol^{-1}$: $C: 12, H: 1, O: 16$]

An organic compound contains $69 \%$ carbon and $4.8 \%$ hydrogen,the remainder being oxygen. Calculate the masses of carbon dioxide and water produced when $0.20 \ g$ of this substance is subjected to complete combustion.

$A$ sample of a pure compound contains $1.15 \ g$ of sodium,$3.01 \times 10^{22}$ atoms of carbon,and $0.1 \ mol$ of oxygen atoms. Its empirical formula is:

In a substance,the number of atoms of $Cr$ and $O$ are $4.8 \times 10^{10}$ and $9.6 \times 10^{10}$ respectively. The empirical formula of the substance is .......