Oxidation Reduction

Introduction
The rusting of metals, the process involved in photography, the way living systems produce and utilize energy, and the operation of a car battery, are but a few examples of a very common and important type of chemical reaction. These chemical changes are all classified as "electron-transfer" or oxidation-reduction reactions. 
The term, oxidation , was derived from the observation that almost all elements reacted with oxygen to form compounds called, oxides. A typical example is the corrosion or rusting of iron as described by the chemical equation: 
4 Fe + 3 O2 -----> 2 Fe2O3 
Reduction, was the term originally used to describe the removal of oxygen from metal ores, which "reduced" the metal ore to pure metal as shown below: 
2 Fe2O3 + 3 C -----> 3 CO2 + 4 Fe 
Based on the two examples above, oxidation can be defined very simply as, the "addition" of oxygen; and reduction, as the "removal" of oxygen. But there is a lot more to "oxidation-reduction", as described in the following sections.