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

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

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 $HCl$. This on reaction with phenol leads to diazotisation coupling.