The rule for determining the oxidation state in a chemical compound.

1) in simple substances (example: H2, O2, Cl2 and the like), the oxidation state is always zero
2) in a complex compound, the sum of the oxidation states of the elements is zero, and in a complex ion it is equal to the charge of the ion
3) for the element iron, the oxidation state is -1: F (-1)
4) for the element oxygen, the oxidation state is -2: O (-2)
however, there are exceptions:
H2O2 – oxidation state -1
OF2 – oxidation state +2
5) for the element hydrogen, the oxidation state is +1: H (+1)
and here’s the exception:
NaH – oxidation state -1