How does the oxidation number of iron change when iron(II) becomes iron(III)?

When iron(II) is converted to iron(III), the oxidation number of the iron atom increases from +2 to +3.12

In the context of an oxidation-reduction reaction, this change represents an oxidation process, as the iron atom loses an additional electron to transition from the Fe²⁺ ion to the Fe³⁺ ion. This increase in oxidation state is a fundamental characteristic of redox reactions, where the participating chemical species undergoes a change in its ability to donate or acquire electrons.134