wt. of \({N}=\left(\frac{42}{100} \times 0.8\right)\, {gm}\)

mole of \(N=\frac{42 \times 0.8}{100 \times 14}=\frac{2.4}{100}\, {~mol}\)

moles of \({NH}_{3}=\frac{2.4}{100}\)

\(2 {NH}_{3}+{H}_{2} {SO}_{4} \rightarrow\left({NH}_{4}\right)_{2} {SO}_{4}\)

\(\quad\downarrow\quad\quad\quad\downarrow\)

\(\frac{2.4}{100}\) \(mole\) \(\quad\frac{1.2}{100}\) \(mole\)

For \({H}_{2} {SO}_{4} \quad \frac{1.2}{100}=1 \times {V}(\ell)\)

\(\Rightarrow {V}_{{H}_{2} {SO}_{4}}=\frac{1.2}{100} \,\ell=12 \,{~m} \ell\)