Identify the reagent involved in Sandmeyer reaction.

Step-by-step solution

The Sandmeyer reaction synthesizes aryl halides or nitriles from aryl diazonium salts by replacing the -N ₂^+ group with a halogen or cyano group using copper(I) salts. CuCN / KCN is a characteristic Sandmeyer reagent, converting aryl diazonium salts to aryl nitriles: Ar-N ₂^+ X ^- + CuCN / KCN Ar-CN + N ₂ + CuX . In contrast, Cu (powder) / HBr pertains to the Gattermann reaction, H₃ PO₃ reduces diazonium salts to arenes, and CH₃ CH₂ OH similarly acts as a reducing agent; none are Sandmeyer reagents. The correct ch