In the titration of $KMnO_{4}$ and oxalic acid in acidic medium,the change in oxidation number of carbon at the end point is

Consider the following equations:
$2 Fe^{2+} + H_2O_2 \rightarrow x A + y B$
(in basic medium)
$2 MnO_4^{-} + 6 H^{+} + 5 H_2O_2 \rightarrow x' C + y' D + z' E$
(in acidic medium)
The sum of the stoichiometric coefficients $x, y, x', y'$ and $z'$ for products $A, B, C, D$ and $E,$ respectively,is............

Observe the following reaction:
$xS_{8\text{(s)}} + yOH^{-}{_{\text{(aq)}}} \rightarrow zS^{2-}{_{\text{(aq)}}} + 2S_2O_3^{2-}{_{\text{(aq)}}} + 6H_2O_{\text{(l)}}$
Find the values of $x, y$ and $z$ respectively.

What is the product of the oxidation of $I^-$ by $MnO_4^-$ in an alkaline medium?

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$PbO_2 + 4HNO_3 (Conc.) \longrightarrow Pb(NO_3)_2 + 2H_2O + O_2$

Explain why the colour of $KMnO_4$ disappears when oxalic acid is added to its solution in acidic medium.