Oxygen always has an oxidation number of - 2 unless it is combined with fluorine or found in the compound peroxide. When in the compound peroxide, it has an oxidation number of?

When oxygen is found is peroxide, it has an oxidation number of - 1.

The chemical formula of hydrogen peroxide is H2O2. We know that hydrogen always has + 1 oxidation state until it forms metal hydrides. So in H2O2, the oxidation state ofhydrogen is + 1.

Now, let oxidation state of oxygen be x. So,

2 * (+1) + 2*x = 0

2 + 2x = 0

2x = - 2

x = - 2 / 2

x = - 1

Hence, the oxidation number of oxygen in peroxides is - 1