Which process involves the gain of electrons?

The process that involves the gain of electrons is reduction. In the context of redox (reduction-oxidation) reactions, reduction specifically refers to the process where an atom, ion, or molecule gains electrons. This results in a decrease in the oxidation state of the substance undergoing reduction.

Reduction is often coupled with oxidation, where another species loses electrons. Therefore, when one substance gains electrons and is reduced, another substance is oxidized by losing those electrons. The concept is fundamental in chemistry, particularly in understanding reactions in electrochemistry and metabolic processes.

Ionization refers to the process of adding or removing electrons to form ions, but it does not specifically imply gaining electrons as a reduction does. Decomposition involves breaking down compounds into simpler substances and does not directly relate to the gaining of electrons. Oxidation, on the other hand, is the opposite of reduction, characterized by the loss of electrons. Thus, reduction is clearly associated with the gain of electrons, distinguishing it from the other processes listed.