Question

What is difference in using alk.KMnO4 and acidic KMnO4???

Answer 1

Equation for reduction of KMnO4 in acidic medium:
8H(+) + MnO4(2-) + 5e(-) ----------> Mn(2+) + 4H2O

In neutral medium:
2H2O + MnO4(-) + 3e(-) ------------> MnO2 + 4OH(-)

In basic medium:
MnO4(-) + e(-) ------------> MnO4(2-)

Thus, you can see that oxidizing effect of KMnO4 is maximum in acidic medium and least in basic medium as in acidic medium the reduction in oxidation state of Mn is max while it is the least in basic medium.

Hence, acidic medium is used when you want strong oxidization and basic when very mild oxidization is required.