What occurs during an oxidation reaction?

During an oxidation reaction, a substance loses electrons. This process is fundamental to redox reactions, where oxidation always accompanies a corresponding reduction. When a substance loses electrons, its oxidation state increases, reflecting the fact that it has undergone oxidation.

For instance, in the reaction of magnesium with oxygen, magnesium loses two electrons to form magnesium ions. The loss of these electrons is what defines the oxidation reaction. Understanding this concept is crucial in various applications, such as in biological systems, energy production, and industrial processes where electron transfer plays a significant role.

The other choices do not align with the definition of oxidation, as gaining electrons pertains to reduction, remaining unchanged does not signify any chemical reaction, and absorbing heat energy relates more to thermodynamics rather than the transfer of electrons in oxidation-reduction reactions.