What happens in an oxidation-reduction reaction?

• A. Electrons are transferred between chemical species, changing the oxidation states
• B. Protons are exchanged between species
• C. Neutrons are emitted
• D. Substances rearrange bonds without electron transfer

Answer: (A)

In a redox reaction, electrons are transferred between species, changing their oxidation states. Oxidation is the loss of electrons, and reduction is the gain of electrons; the donor becomes oxidized (reducing agent) and the acceptor becomes reduced (oxidizing agent). For example, when iron metal reacts with oxygen, iron loses electrons and becomes iron ions, while oxygen gains electrons and is reduced.

Protons being exchanged happens in acid-base chemistry, not redox. Neutrons emitted involve nuclear processes, not chemical reactions. Substances that simply rearrange bonds without any electron transfer are not undergoing a redox change, since no oxidation state changes occur.