The following reaction is named as:

\(\mathrm{Ar}^{+} \mathrm{Cl}_2 \mathrm{Cl}^{-} \xrightarrow{\mathrm{Cu}, \quad \mathrm{HCl}} \mathrm{ArCl}+\mathrm{N}_2+\mathrm{CuCl}\)

1. Sandmeyer reaction
2. Gattermann reaction
3. Claisen reaction
4. Carbylamine reaction

Hint: Alternative method for introducing chlorine or bromine in the benzene ring
This reaction is called Gattermann reaction. In this reaction, Cl, Br and CN can be introduced into the benzene ring by simply treating diazonium salts with HCI, HBr, KCN, respectively in presence of copper powder instead of using Cu (l) salts. The reaction is as follows: