In nitration of benzene using conc. $H_{2}S{O}_4$ and conc. $HN{O}_3$, the role of nitric acid is

The correct option is B a base
Nitration is electrophilic substitution reaction; in its first step $HN{O}_3$ takes protons from sulphuric acid and then forms $-N{O}_2^{+}$, so here $HN{O}_3$ acts as base.
$HN{O}_3+H_{2}S{O}_4^{-}\to H_{2}O+\underset{\text{Nitration ion}\left(\text{attacking species}\right)}{N{O}_2^{+}}+HS{O}_4^{-}$
$H_{2}S{O}_4$ serves as the acid and $HN{O}_3$ as the base.
Hence, the correct answer is option (b).