Which one of the following compounds does not decolourise an acidified aqueous solution of $KMnO_4$?

The following reaction describes the rusting of iron:
$4Fe + 3O_2 \to 4Fe^{3+} + 6O^{2-}$
Which one of the following statements is incorrect?

Which of the following reactions is a decomposition redox reaction?

To measure the quantity of $MnCl_2$ dissolved in an aqueous solution,it was completely converted to $KMnO_4$ using the reaction,
$MnCl_2 + K_2S_2O_8 + H_2O \longrightarrow KMnO_4 + H_2SO_4 + HCl$ (equation not balanced).
Few drops of concentrated $HCl$ were added to this solution and gently warmed. Further,oxalic acid $(225 \ mg)$ was added in portions till the colour of the permanganate ion disappeared. The quantity of $MnCl_2$ (in $mg$) present in the initial solution is . . . . . . . . . (Atomic weights in $g \ mol^{-1}: Mn = 55, Cl = 35.5$ )

$x, y$ and $z$ are respectively:
$MnO_4^- + x e^- \xrightarrow{\text{Alkaline medium}} MnO_4^{2-}$
$MnO_4^- + y e^- \xrightarrow{\text{Acidic medium}} Mn^{2+}$
$MnO_4^- + z e^- \xrightarrow{\text{Neutral medium}} MnO_2$

Assign $A, B, C, D$ from the given type of reaction.
$KI + BiI_3 \downarrow \longrightarrow K[BiI_4]$