Ozone is determined quantitatively by first reacting it with excess of KI at a particular pH and then titrating the $\mathrm{I}_2$ thus, liberated with a suitable titrant. The pH of the reaction and the titrant used in the titration are respectively.

$$\mathrm{MnO}_4^{-}$$ is good oxidising agent in different medium changing to

$$\mathrm{MnO}_4^{-} \rightarrow \mathrm{Mn}^{2+} \rightarrow \mathrm{MnO}_4^{2-} \rightarrow \mathrm{MnO}_2 \rightarrow \mathrm{Mn}_2 \mathrm{O}_3$$

Change in oxidation number respectively are :

The standard $$E_{\text {red }}^{\circ}$$ values of $$A, B$$ and $$C$$ are $$+0.52 \mathrm{~V},-23.6 \mathrm{~V},-0.44 \mathrm{~V}$$ respectively. The order of their reducing power is