The product A formed in the following reaction is:

Diazotization: The process of conversion of a primary aromatic amino compound into a diazonium salt is known as diazotization. This process is carried out by adding an aqueous solution of sodium nitrite to a solution of primary aromatic amine (e.g., aniline) in excess of $\mathrm{HCl}$ at a temperature below $5^{°}\mathrm{C}$.

Decomposition of benzene diazonium chloride by using ${\mathrm{Cu}}_2{\mathrm{Cl}}_2/\mathrm{HCl}$ to form chlorobenzene is known as sandmeyer's reaction.