Here's why:

* Oxygen is more electronegative than hydrogen. This means oxygen has a stronger pull on the shared electrons in the H-O bond.

* Oxygen typically has an oxidation state of -2 in most compounds, except in peroxides.

* In hydrogen peroxide, each oxygen atom has an oxidation state of -1. This is because the two oxygen atoms are bonded to each other, and the electrons in that bond are shared equally.

* To balance the charges, each hydrogen atom must have an oxidation state of +1.

Therefore, the overall oxidation state of hydrogen peroxide is:

2(+1) + 2(-1) = 0