Acidified potassium permanganate solution is decolourised by

Balance the following equations in basic medium by the ion-electron method and identify the oxidising agent and the reducing agent.
$(a)$ $P_{4(s)} + OH^{-}_{(aq)} \rightarrow PH_{3(g)} + H_{2}P{O_{2}}^{-}_{(aq)}$
$(b)$ $N_{2}H_{4(l)} + Cl{O_{3}}^{-}_{(aq)} \rightarrow NO_{(g)} + Cl^{-}_{(g)}$
$(c)$ $Cl_{2}O_{7(g)} + H_{2}O_{2(aq)} \rightarrow Cl{O_{2}}^{-}_{(aq)} + O_{2(g)} + H^{+}_{(aq)}$

The number of moles of $KMnO_4$ required to oxidize one equivalent of $KI$ in the presence of sulphuric acid is

In acidic medium, one mole each of $MnO_4^-$ and $Cr_2O_7^{2-}$ is reduced by $x$ and $y$ moles of ferrous ions $(Fe^{2+})$ respectively. The sum of $x$ and $y$ is:

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$Pb(NO_3)_2 + H_2SO_4 \longrightarrow PbSO_4 \downarrow + 2HNO_3$

$H_2S$ acts only as a reducing agent while $SO_2$ can act both as a reducing and oxidizing agent because