The correct option is A Mn2+<MnO2<MnO−4
More the oxidation state of the Mn, more will be oxidizing power.
As Mn2+ has +2 oxidation state, MnO2 has +4 oxidation state of Mn whereas MnO−4 has +7 oxidation state of the Mn.
So, as MnO−4 has maximum oxidation state of Mn, it is the strongest oxidizing agent and the order of increasing strength as an oxidizing agent is as follows:
Mn2+<MnO2<MnO−4