An acidic solution of MnO_4^{2-}_{(aq)} undergoes the reaction shown below:

The marking scheme gives answer C. In $MnO_4^{2-}$, Mn is +6. In $MnO_4^-$, Mn is +7 (oxidised). In $MnO_2$, Mn is +4 (reduced). So $MnO_4^{2-}$ is both oxidised (to $MnO_4^-$) and reduced (to $MnO_2$) — this is disproportionation. The statement that $MnO_4^{2-}$ is oxidised to $MnO_4^-$ is correct.