What occurs when an atom loses an electron?

When an atom loses an electron, it undergoes oxidation. Oxidation is defined as the process in which an atom, ion, or molecule loses electrons, resulting in an increase in oxidation state. This is an essential concept in chemistry and relates to redox reactions, which involve both oxidation and reduction processes.

While reduction refers to the gain of electrons (and hence a decrease in oxidation state), it is crucial to understand that oxidation specifically identifies the electron loss aspect of the redox process.

Ionization is another related concept, but it specifically refers to the process of forming ions, which can occur through various means, not just electron loss. Hydration pertains to the interaction of water with a substance and does not directly relate to changes in electron count or oxidation states.

In summary, the process resulting from the loss of an electron is oxidation, making it the correct answer.