A Redox reaction is a type of chemical reaction in which both oxidation and reduction occur simultaneously, which involves a transfer of electrons between two species. Initially, oxidation was used to describe the addition of oxygen to an element or a compound. The following reactions represent oxidation processes according to the limited definition of oxidation: 1. * 2Mg(s) + o2(g) 2MgO(s) 2. * S(s) + O2(g) SO2(g)