The change in oxidation state of Mn element in the reaction , 3MnO4²- + 4H+→ MnO2+2MnO4- + 2H2O is? Please help me, thanks.

Permanganate ion is reduced from ##Mn(VII+)## to ##Mn(IV+)## in the oxide.

The reduction equation is:

##MnO_4^(-) + 4H^+ + 3e^(-) rarr MnO_2 + 2H_2O##

This is balanced with respect to mass and charge. However, permanganate is normally reduced to ##Mn^(2+)##, which is almost colourless. In fact, this reduction reaction is self indicating in that permanganate is intensely coloured.