What is an oxidation reaction?
Very basically, an oxidation reaction is one which involves the loss of electrons.
Use this mnemonic to remember the difference between oxidation and reduction reactions: OIL RIG
Oxidation Is Loss
Reduction Is Gain
Here is an example of an oxidation reaction
In this reaction, the magnesium has lost two electrons - this is, thus, an oxidation reaction. Notice how it is different if the reverse reaction was to take place:
In this reaction, magnesium has gained two electrons - this is, thus, a reduction reaction.