The oxidation states not shown by Mn in given reaction is :

$$ 3 \mathrm{MnO}_4^{2-}+4 \mathrm{H}^{+} \longrightarrow 2 \mathrm{MnO}_4^{-}+\mathrm{MnO}_2+2 \mathrm{H}_2 \mathrm{O} $$

A. +6

B. +2

C. +4

D. +7

E. +3

Choose the most appropriate answer from the options given below :

Which reaction is NOT a redox reaction?

The correct option for a redox couple is:

On balancing the given redox reaction,

$$\mathrm{aCr}_{2} \mathrm{O}_{7}^{2-}+\mathrm{bSO}_{3}^{2-}(\mathrm{aq})+\mathrm{cH}^{+}(\mathrm{aq}) \rightarrow 2 \mathrm{aCr}^{3+}(\mathrm{aq})+\mathrm{bSO}_{4}^{2-}(\mathrm{aq})+\frac{\mathrm{c}}{2} \mathrm{H}_{2} \mathrm{O}(\ell)$$

the coefficients $$\mathrm{a}, \mathrm{b}$$ and $$\mathrm{c}$$ are found to be, respectively -