IIT JEE Advanced 2011 Paper 2

In acidic medium, permanganate acts as a strong oxidising agent because of the reaction
8H++5e−+MnO4− → Mn2++4H2O
Thus, 5 electrons involved in acidic medium reaction.
In neutral medium, permanganate acts as a moderate oxidising agent because of the reaction
2H2O+3e−+MnO4− → MnO2+4OH−
Thus, 3 electrons involved in neutral medium reaction.
In alkaline medium, potassium permanganate acts in a similar way as in neutral medium.
2H2O+3e−+MnO4− → MnO2+4OH−
Thus, 3 electrons involved in alkaline medium reaction.