Give reason: Nitration of benzene is not possible with only $HNO_3$.

(N/A) Benzene possesses characteristic aromatic stability due to delocalized $\pi$-electrons.
To initiate nitration,a strong electrophile is required to attack the stable $\pi$-electron cloud.
$HNO_3$ alone does not generate a sufficiently strong electrophile $(NO_2^+)$ in high enough concentration to overcome the resonance energy of benzene.
Therefore,a mixture of concentrated $HNO_3$ and concentrated $H_2SO_4$ is used to generate the strong electrophile $NO_2^+$.