By how much is oxidizing power of $MnO_4^-/Mn^{+2}$ couple decreases if the $H^+$ concentration is decreased from 1M to $10^{-4}$M at $25^{\large\circ}C$ .Assume other species have no change in concentration.

Question

$\begin{array}{1 1}(a)\;0.37V\\(b)\;0.35V\\(c)\;0.4V\\(d)\;0.28V\end{array}$