Which of the following best describes the key characteristic of an oxidation–reduction (redox) reaction?

• A. Release of energy in the form of heat
• B. Formation of a precipitate
• C. Change in physical state of the reactants
• D. Transfer of electrons between reactants

Answer: (D)

Verified step by step guidance

1. Understand that oxidation–reduction (redox) reactions involve changes in the oxidation states of atoms within the reactants.
2. Recognize that the key feature of redox reactions is the transfer of electrons from one species to another, which causes one species to be oxidized (lose electrons) and another to be reduced (gain electrons).
3. Note that other options like release of heat, formation of a precipitate, or change in physical state are not defining characteristics of redox reactions, although they may occur in some reactions.
4. Focus on the electron transfer process as the fundamental criterion that distinguishes redox reactions from other types of chemical reactions.
5. Summarize that the best description of a redox reaction is the transfer of electrons between reactants, which directly affects their oxidation states.