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 $HCl$ at a temperature below ${5}^{°}C$.

Decomposition of benzene diazonium chloride by using ${Cu}_{2}{Cl}_{2} / HCl$ to form chlorobenzene is known as sandmeyer's reaction.