How many moles of electrons are needed to convert one mole of nitrate ion to hydrazine?

Which of the following reagents causes the aqueous colored solution of acidic $KMnO_4$ to become colorless?

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$4FeCr_2O_4 + 8Na_2CO_3 + 7O_2 \longrightarrow 2Fe_2O_3 + 8Na_2CrO_4 + 8CO_2$

$MnO_4^{-}$ oxidises $(i)$ oxalate ion in acidic medium at $333 \ K$ and $(ii)$ $HCl$. For balanced chemical equations,the ratios $[MnO_4^{-} : C_2O_4^{2-}]$ in $(i)$ and $[MnO_4^{-} : HCl]$ in $(ii)$ respectively are

Manganese ions $(Mn^{2+})$ can be oxidised by persulphate ions $(S_2O_8^{2-})$ according to the following half-equations:
$S_2O_8^{2-} + 2e^- \longrightarrow 2SO_4^{2-}$
$Mn^{2+} + 4H_2O \longrightarrow MnO_4^- + 8H^+ + 5e^-$
How many moles of $S_2O_8^{2-}$ are required to oxidise $1 \ mole$ of $Mn^{2+}$?

In neutral or faintly alkaline medium,$KMnO_4$ being a powerful oxidant can oxidize thiosulphate almost quantitatively to sulphate. In this reaction,the overall change in the oxidation state of manganese will be: