While sulfur dioxide and hydrogen peroxide can act as oxidizing as well as reducing agents in their reactions, ozone and nitric acid act only as oxidants. This is because:

(a) In SO₂ and H₂O₂, S and O are in their lowest oxidation state.
(b) In O₃ and HNO₃, N and O are in their highest oxidation state.
(c) In SO₂ and H₂O₂, S and O are in their lowest oxidation state, and in O₃ and HNO₃, N and O are in their highest oxidation state.
(d) Both (a) and (b).