How many electrons are involved in the reduction of $KMnO_4$ in a basic medium?

$KMnO_4$ in basic medium is reduced to

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$S + HNO_3 \, (Dil.) \longrightarrow H_2SO_4 + NO \uparrow $

Balance the following redox reactions by the ion-electron method:
$(a)$ $MnO_4^-(aq) + I^{-}(aq) \rightarrow MnO_2(s) + I_2(s)$ (in basic medium)
$(b)$ $MnO_4^-(aq) + SO_2(g) \rightarrow Mn^{2+}(aq) + HSO_4^-(aq)$ (in acidic solution)
$(c)$ $H_2O_2(aq) + Fe^{2+}(aq) \rightarrow Fe^{3+}(aq) + H_2O(l)$ (in acidic solution)
$(d)$ $Cr_2O_7^{2-} + SO_2(g) \rightarrow Cr^{3+}(aq) + SO_4^{2-}(aq)$ (in acidic solution)

In the following reaction $yMnO_4^- + xH^{+} + C_2O_4^{2-} \to yMn^{2+} + 2CO_2 + \frac{x}{2}H_2O$,the values of $x$ and $y$ are:

Which of the following reactions is a redox reaction?