What characterizes a redox reaction?

A redox reaction, short for reduction-oxidation reaction, is fundamentally 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, which entails the gain of those electrons. This electron transfer is essential because it dictates the change in oxidation states of the elements involved, highlighting the fundamental process that defines redox chemistry.

While the addition of oxygen can occur in certain redox reactions, it is not a defining characteristic. The release of heat may happen in exothermic redox reactions, but it is not universally applicable to all redox processes. Similarly, the formation of a gas can occur in some reactions, but it is not a requirement for a redox reaction, as many redox reactions involve solid, liquid, or aqueous states without producing gas. Thus, the key feature of redox reactions is the electron transfer, which plays a pivotal role in understanding various chemical processes and applications.