The E° value for the Mn3+/Mn2+ couple is more positive than that of Cr3+/Cr2+ or Fe3+/Fe2+ due to change of [2024]
(3)
Mn25⇒[Ar]3d54s2
Mn3+⇒[Ar] 3d4
Mn2+⇒[Ar] 3d5
As d5 is a half-filled electronic configuration, it is highly stable configuration. Thus, Mn3+ has high tendency to get reduced to Mn2+.