b
Proton donor is acids and proton acceptor is bases. Conc. \(\mathrm{H}_{2} \mathrm{SO}_{4}\) and conc. HNO \(_{3}\) react in the following manner:

\(\mathrm{HNO}_{3}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{H}_{2} \mathrm{NO}_{3}^{+}+\mathrm{HSO}_{4}^{-}\)

\(\mathrm{H}_{2} \mathrm{NO}_{3}^{+} \rightarrow \mathrm{NO}_{2}^{+}+\mathrm{H}_{2} \mathrm{O}\)

Hence, in this reaction HNO \(_{3}\) acts as a base and \(\mathrm{H}_{2} \mathrm{SO}_{4}\) as an acid.