Final answer:
Oxidation involves the loss of electrons, while reduction involves the gain of electrons. They always occur together in chemical reactions.
Step-by-step explanation:
Oxidation is defined as the loss of electrons by an atom, while reduction is defined as the gain of electrons by an atom. Therefore, the correct statement among the options is a) Oxidation involves gaining electrons. However, it is important to note that oxidation and reduction always occur together in chemical reactions, which are called oxidation-reduction reactions, or redox reactions.