Iodine is released when potassium iodide reacts with

$I^{-}(aq.) + MnO_4^{-}(aq.) \xrightarrow{H^{+}} X + Mn^{2+}(aq.)$
$I^{-}(aq.) + MnO_4^{-}(aq.) \xrightarrow{\text{Neutral or weakly } OH^{-}} Y + MnO_2$
$MnO_4^{-}(aq.) + Mn^{2+}(aq.) \xrightarrow{ZnSO_4} Z + 4H^{+}$
Products $X, Y$ and $Z$ are respectively :

If zinc pieces are added to yellow $FeCl_3$ solution,it turns to very light green. It is because

Why do the following reactions proceed differently? $Pb_{3}O_{4} + 8HCl \rightarrow 3PbCl_{2} + Cl_{2} + 4H_{2}O$ and $Pb_{3}O_{4} + 4HNO_{3} \rightarrow 2Pb(NO_{3})_{2} + PbO_{2} + 2H_{2}O$

Which of the following reactions is not a redox reaction?

The autocatalyst in the redox reaction involving acidified potassium permanganate and oxalic acid is