Oxidation-reduction is another class of reaction that we need to know about. What is oxidation-reduction? It is a reaction where electrons are transferred.
Oxidation and Reduction
Oxidation and reduction are complementary processes. When one occurs, the other must also occur.
One way to determine whether oxidation-reduction has occurred or not is to see if the oxidation number of a species has changed. Oxidation numbers also tell us what has been oxidised and what has been reduced.