A species whose oxidation number increases in a reaction is oxidized (reducing reagents or reactant).
For example, balanced chemical
reaction: 2KClO₃ → 2KCl + 3O₂.
Oxygen in the
reactant state has oxidation number -2 (+1 + 5 + 3 · x = 0) and it is
oxidized to 0 (in molecule of oxygen) in the product state.
