Key Idea Proton donor are acids and proton acceptor are bases. Conc. H2SO4 and conc. HNO3 react in the following manner : base HNO3+ acid H2SO4⟶H2NO3++HSO4−H2NO3+⟶ nitronium ion NO2++H2O Hence, in this reaction HNO3 acts as a base and H2SO4 as an acid.