Nitrobenzene can be prepared from benzene by using a mixutre of...

Key Idea Proton donor are acids and proton acceptor are bases. Conc. $\mathrm{H}_2 \mathrm{SO}_4$ and conc. $\mathrm{HNO}_3$ react in the following manner : $$\begin{aligned}& \underset{\text{ base }}{\mathrm{HNO}_3}+\underset{\text{ acid }}{\mathrm{H}_{2} \mathrm{SO}_{4}} \longrightarrow \mathrm{H}_{2} \mathrm{NO}_{3}^{+}+\mathrm{HSO}_{4}^{-} \\ & \mathrm{H}_{2} \mathrm{NO}_{3}^{+} \longrightarrow \underset{\substack{\text{ nitronium }\\ \text{ ion }}}{ \mathrm{NO}_{2}^{+}}+\mathrm{H}_{2} \mathrm{O}\\ & \end{aligned}$$Hence, in $this reaction \mathrm{HNO}_{3}acts as a base and \mathrm{H}_{2}\mathrm{SO}_{4} as an acid.