The oxidation number of ##”H”## is +1. The oxidation number of ##”O”## is -1.

You assign to the in a compound by using the Rules for Oxidation Numbers.

The important rules for this problem are:

1. The oxidation number of ##”H”## is +1, but it is -1 in when combined with less electronegative elements.

2. The oxidation number of ##”O”## in is usually -2, but it is -1 in peroxides.

3. The sum of the oxidation numbers of all the atoms in a neutral compound is 0.

The oxidation number of ##”H”## is +1 (Rule 1).

If you know that ##”H”_2″O”_2## is hydrogen peroxide, you can immediately assign oxygen the ON = -1.

If you don’t know that ##”H”_2″O”_2## is hydrogen peroxide, you can use Rule 3.

The oxidation number of ##”H”## is +1. For two ##”H”## atoms, the sum is +2.

Since ##”H”_2″O”_2## has no charge, the total oxidation number of the two ##”O”## atoms must be -2.

The oxidation number of one oxygen atom must be -1.