The oxidation state of Fe in `Fe_(3)O_(4)` is :

Explanation

Let the oxidation state of Fe in `Fe_(3)O_(4)` be x.
`3x+[4(-2)]=0 or x=+8//3`
Thus, oxidation state of Fe in `Fe_(3)O_(4)` is `+8//3`. This is the average oxidation state of Fe in `Fe_(3)O_(4)`. Actually, `Fe_(3)O_(4)` is made up of equimolar quantity of `FeO and Fe_(2)O_(3)`.