What does oxidation refer to in a chemical reaction?

Oxidation in a chemical reaction refers to the loss of electrons by a substance. When a substance undergoes oxidation, it typically increases its oxidation state. This process is often associated with reactions where a substance reacts with oxygen, but more fundamentally, it is characterized by the transfer of electrons.

For example, in the reaction of iron with oxygen to form iron oxide, iron loses electrons (is oxidized) while oxygen gains those electrons (is reduced). This fundamental concept is key to understanding redox (reduction-oxidation) reactions, where one species is oxidized and another is reduced.

Understanding this definition of oxidation is crucial for analyzing various chemical processes, particularly in organic chemistry and electrochemistry, where electron transfer plays a significant role. The other concepts involving protons and the gain of electrons refer to different processes and are not applicable to the definition of oxidation.