Oxidation is the opposite of reduction. A reduction-reaction always comes together with an oxidation-reaction. Oxidation and reduction together are called redox (reduction and oxidation). Oxygen does not have to be present in a reaction for it to be a redox-reaction.
Oxidation is the loss of electrons.
In terms of oxygen transfer
When one of the reactants is oxygen, then oxidation is a gain of oxygen. Reduction is a loss of oxygen. For example:
- Fe2O3 + 3CO → 2Fe + 3CO2
Both reduction and oxidation go on at the same time which is a redox-reaction. The loss of hydrogen atoms and the gain of oxygen atoms is known as oxidation. The gain of hydrogen atoms and the loss of oxygen atoms is known as reduction. Oxidation is gain of oxygen atoms and reduction is gain of hydrogen atoms.