Oxidation is a process when an atom, a group of atoms, or an ion loses electrons.
For example,
Cu⁰ -------> Cu⁺² + 2e⁻. This is an oxidation process.
As we can see an oxidation number was 0, and it became +2. The oxidation number is increased. Oxidation number of the atom, when an atom has undergone oxidation, increases.
