Hydrolysis of a diazonium salt occurs under acidic conditions. When a diazonium salt, such as benzenediazonium chloride, is treated with water in the presence of acid (HCl), it undergoes hydrolysis to form phenol. In this reaction, the diazo group (-N₂⁺) is replaced by a hydroxyl group (-OH⁻) on the benzene ring. The resulting product is phenol, which is a hydroxy-substituted aromatic compound. This reaction is a part of the Sandmeyer reaction, and it provides a method for the synthesis of phenols from diazonium salts under mild acidic conditions.