ACS Chemistry Practice Exam 2025 – The All-in-One Guide to Exam Success!

A redox reaction, short for reduction-oxidation reaction, is characterized by the transfer of electrons between reactants. In such reactions, one species undergoes oxidation, which involves the loss of electrons, while another species undergoes reduction, involving the gain of electrons. This transfer of electrons is what fundamentally defines redox reactions, making option C the correct choice.

The involvement of covalent bonds represents a different kind of interaction that may occur in various chemical reactions but does not specifically define redox processes. Proton transfer reactions relate more to acid-base chemistry rather than redox reactions, where the focus is on electron movement rather than proton exchange. Finally, while some redox reactions can be facilitated at high temperatures, temperature alone does not define the reaction as redox; it is the electron transfer that is the key identifying feature. Thus, the essence of redox reactions lies explicitly in the transfer of electrons, which is perfectly captured in option C.