Which of the following statements is true regarding a redox reaction?

In a redox reaction, the fundamental principle is that electrons are transferred between reactants, leading to a change in oxidation states. When one reactant loses electrons, it undergoes oxidation, while the reactant that gains electrons experiences reduction. This transfer of electrons is what makes option A a correct statement about redox reactions, as they are inherently about the exchange of electrons between different chemical species.

The other statements do not accurately represent the nature of redox reactions. For instance, while oxygen often participates in many types of redox reactions, it is not a requirement, as these reactions can occur with a variety of different elements and compounds. Additionally, redox reactions are not limited to anaerobic processes; they are fundamental to both aerobic and anaerobic respiration. Lastly, redox reactions are not strictly irreversible; many can proceed in both directions under certain conditions, depending on the reaction environment and the concentrations of the reactants and products involved.