d
In an unknown compounds containing \(N\) and \(H\)

given \(\%\) of \(H\) \(= 12.5\%\)

\(\therefore \) \(\%\) of \(N\) \(= 100-12.5 = 87.5\%\)

Element	Percentage	Atomic ratio	Simple ratio
\(H\)	\(12.5\%\)	\(\frac{12.5}{1}=12.5\)	\(\frac{12.5}{6.25}=2\)
\(N\)	\(87.5\%\)	\(\frac{87.5}{14}=6.25\)	\(\frac{6.25}{6.25}=1\)

\(2 \times\) vapour density \(=\) Mol. wt \(= 16 \times 2 = 32.\)

Molecular formula \(= n \times\) empirical formula mass

\(n = \frac{{32}}{{16}} = 2\)

\(\therefore \) Molecular formula of the compound will be \(= (NH_2)_2\)

\(= N_2H_4\)