Define oxidation, reduction, and oxidation number. Describe how oxidation and reduction affect the oxidation number of an element.

Oxidation: the loss of electrons

Reduction: the gain of electrons

Oxidation number: the charge based on the number of electrons assigned to an atom as compared to the neutral atom

Explanation:

The oxidation number of a neutral atom is zero. When the atom is oxidized, it loses electrons (which have a negative charge), so the oxidation number goes up. When the atom is reduced, it gains electron (it gains negative charge), so the oxidation number goes down.