The products A and B formed in the following reaction scheme are respectively

Benzene reacts with concentrated nitric acid at $323-333 \mathrm{K}$ in the presence of concentrated sulphuric acid to form nitrobenzene. This converts to Aniline on reaction with $\mathrm{Sn}/\mathrm{HCl}$.

The chemical process used in converting a primary aromatic amine into the corresponding diazonium salt of the amine is commonly referred to as diazotization by using sodium nitrite and $\mathrm{HCl}$. This on reaction with phenol leads to diazotisation coupling.