The Oxidation number of ‘Fe’ in Fe₃O₄

The oxidation state of Fe in Fe₃O₄ is calculated as:

$$\begin{gathered} 3(\mathrm{oxidation} \mathrm{state} \mathrm{of} \mathrm{Fe})+4(-2)=0 \\ 3(\mathrm{oxidation} \mathrm{state} \mathrm{of} \mathrm{Fe})=8 \\ \mathrm{oxidation} \mathrm{state} \mathrm{of} \mathrm{Fe}=2.66 \end{gathered}$$