Oxidation • Reduction

One of the fundamental principles of chemical reactions. An increase in oxidation number corresponds to oxidation, and a decrease corresponds to reduction. Efforts to define oxidation and reduction have been a central topic since the birth of chemistry, and they can be summarized chronologically as follows: As the term 'oxidation' suggests, in the early days, it was defined as gaining oxygen, and reduction as losing oxygen. However, there were reactions that were clearly oxidation-reduction reactions by characteristic but did not involve oxygen. These reactions were naturally difficult to define based on oxygen. To explain these, reduction was defined as gaining electrons, and oxidation as losing them. In any chemical reaction equation, if one substance is oxidized, another substance must be reduced. (Simultaneity of Oxidation-Reduction) This is because electrons are neither lost nor created.