What describes a chemical reaction within an electrolyte that leaves a metal with excess electrons?

The phenomenon where a metal gains excess electrons in a chemical reaction within an electrolyte is best described by the term "reduction." In a reduction reaction, a substance acquires electrons, which decreases its oxidation state. When a metal is in the presence of an electrolyte and undergoes a reduction process, it effectively becomes more negative due to the gained electrons, resulting in an excess of negative charge.

Electrode potential refers to the voltage created by the electron flow in a half-cell but does not specifically describe the process of a metal gaining electrons. Oxidation, in contrast, is the process of a substance losing electrons, which leads to an increase in oxidation state, the opposite of what is happening here. Ionization pertains to atoms or molecules gaining or losing electrons to form ions, but it does not specifically address the transfer of electrons and the resulting charge states related to the metal in the electrolyte context. Thus, reduction is the correct choice as it accurately encompasses the mechanism of a metal acquiring excess electrons.