In alkaline medium, the reduction of permanganate anion involves a gain of _______ electrons.

In strong Alkaline medium 
${\mathrm{MnO}}_4^{-}\text{changes to }{\mathrm{MnO}}_4^{-2}$
Change in oxidation state is 1
no.of e^- gained=1
In weak Alkaline medium 
${\mathrm{MnO}}_4^{-}\text{changes to }{\mathrm{MnO}}_2$
Change in oxidation state is 3
$\therefore$ no.of e^- gained=3