Nitrobenzene can be prepared by heating with a mixture of concentrated $HN{O}_3$ and concentrated $H_{2}S{O}_4$. In this nitrating mixture, $HN{O}_3$, acts as

The correct option is A A base
In preparation of nitrobenzene $H_{2}S{O}_4$, protanates nitric acid. So, $H_{2}S{O}_4$, acts as an acid while $HN{O}_3$ which accepts proton, acts as a base.