What element is being oxidized in the following redox reaction?

H2O2 (l) + ClO2 (aq) → ClO2 (aq) + O2 (g)

The O is being oxidized, but at the same time, is being reducted.

Explanation:

H₂O₂ (l) + ClO₂ (aq) → ClO₂ (aq) + O₂ (g)

In this reaction, we have 4 compounds:

Hydrogen peroxide

Chlorine dioxide (twice)

Oxygen

In both dioxide, the Cl acts with + 4 in oxidation state; the oxygen acts with - 2.

Oxgen in ground state has 0, as oxidation number.

In peroxide, the H acts with + 1 but the oxygen acts with - 1.

Peroxide is making the oxidation number from the O in the ClO₂, to decrease (reduction) and to increase in the O, at the ground state.

Hydrogen peroxide is a good reducing and oxidizing agent at the same time.