The reduction reaction that occurs in an electrochemical reaction:

In an electrochemical reaction, the reduction reaction specifically involves the gain of electrons. Reduction is defined as the process where an atom, ion, or molecule gains electrons, leading to a decrease in oxidation state. In the context of a galvanic cell or electrolytic cell, this gain of electrons typically occurs at the cathode, which is the electrode where reduction happens. The electrons that are gained are often derived from the anode, where oxidation occurs, but the fundamental characteristic of reduction is the acceptance of electrons.

Therefore, in summarizing why it is correct to say that the reduction reaction involves the gain of electrons, it is important to note that this characteristic is at the core of how reduction is defined in electrochemistry.