A gaseous compound of nitrogen and hydrogen contains 12.5 mass% of hydrogen. The density of the compound relative to hydrogen is 16. The molecular formula of the compound is

$\mathrm{N}:\mathrm{H}::\frac{87.5}{14}:\frac{12.5}{1}::6.25:12.5::1:2$

Empirical Formula: ${\mathrm{NH}}_2$

Molar empirical formula mass$= 16 \mathrm{g} {\mathrm{mol}}^{-1}$

Molar mass $=(2\times$vapor density $)\mathrm{gmol}=2\times 16\mathrm{g}{\mathrm{mol}}^{-1}$

Molecular formula ${({\mathrm{NH}}_2 )}_2$, i.e. ${\mathrm{N}}_2{\mathrm{H}}_4$ .