Which statement best describes the process of oxidation-reduction reactions?

• A. Electrons are transferred between chemical species, changing oxidation states
• B. Protons are exchanged without electron transfer
• C. Atoms rearrange while oxidation states stay the same
• D. Neutrons vary to balance charge

Answer: (A)

Redox chemistry centers on the transfer of electrons between species, which changes their oxidation states. When a substance is oxidized, it loses electrons and its oxidation state increases; when another species is reduced, it gains those electrons and its oxidation state decreases. The oxidation state is just a bookkeeping way to track that electron transfer in chemical reactions. If no electrons are moved, oxidation states stay the same. Proton exchange without electron transfer describes acid-base chemistry, not redox. A rearrangement of atoms with no change in oxidation states is simply a structural change without electron transfer. Neutrons changing would point to nuclear changes, not chemical redox. Therefore, the statement about electrons being transferred and oxidation states changing best describes oxidation–reduction reactions.