Identify\('X'\)

The correct answer is option 4.

The reaction given will be as follows:

When \(H_3PO_2\) reacts with diazonium salt, reduction occurs by the removal of the \(N_2\) molecule and replacing it with \(H\) atom. Here, \(H_3PO_2\) acts as a reducing agent. The bromine in the system does not participate in this reaction and remains unaltered. This property of \(H_3PO_2\) to selectively reduce diazonium salts without affecting the other functional groups is very much utilized in the field of organic synthesis