Among the following, the reaction or reactions that can be classified as oxidation reduction is or are 

I. $$\text{Cr}_2\text{O}_7^{2-}(aq) + 2\text{OH}^-(aq) \to 2\text{CrO}_4^{2-} + \text{H}_2\text{O}(l)$$

II. $$\text{SiCl}_4(l) + 2\text{Mg}(s) \to 2\text{MgCl}_2(l) + \text{Si}(s)$$ 

III. $$6\text{Cl}_2(l) + 12\text{KOH}(l) \to 2\text{KClO}_3(s) + 10\text{KCl} + 6\text{H}_2\text{O}(l)$$

IV. $$2\text{H}_2\text{O}_2 \to 2\text{H}_2\text{O}(l) + \text{O}_2(g)$$