The reaction which occur in the Galvanic cell is
 $\begin{array}{c}{\mathrm{MnO}}_4^{-}+8{\mathrm{H}}^{+}+5{\mathrm{Fe}}^{2+}⟶{\mathrm{Mn}}^{2+}+5{\mathrm{Fe}}^{3+}+4{\mathrm{H}}_2\mathrm{O}\\ {\mathrm{E}}^{\circ }\left({\mathrm{MnO}}_4^{-},{\mathrm{Mn}}^{2+},{\mathrm{H}}^{+}\mid \mathrm{Pt}\right)=1.51\mathrm{V}\text{ and }\\ {\mathrm{E}}^{\circ }\left({\mathrm{Fe}}^{3+},{\mathrm{Fe}}^{2+}\mid \mathrm{Pt}\right)=0.77\mathrm{V}\end{array}$
(Q). The other concentrations are kept at unity except reducing $\left[{\mathrm{Mn}}^{2+}\right]$to 0.50 M, the emf of the cell is increased by