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

Balance the following equations by the oxidation number method:
$(a) Fe^{+2} + H^{+} + Cr_2O_7^{-2} \to Cr^{+3} + Fe^{+3} + H_2O$
$(b) I_2 + NO_3^- \to NO_2 + IO_3^-$
$(c) I_2 + S_2O_3^{-2} \to I^{-} + S_4O_6^{-2}$
$(d) MnO_4^- + C_2O_4^{-2} \to Mn^{+2} + CO_2$

$HNO_2$ acts as

Consider the following reactions (unbalanced):
$Zn +$ hot conc. $H_2SO_4 \rightarrow G + R + X$
$Zn +$ conc. $NaOH \rightarrow T + Q$
$G + H_2S + NH_4OH \rightarrow Z$ (a precipitate) $+ X + Y$
Choose the correct option$(s)$.
$(1)$ The oxidation state of $Zn$ in $T$ is $+1$
$(2)$ Bond order of $Q$ is $1$ in its ground state
$(3)$ $Z$ is dirty white in colour
$(4)$ $R$ is a $V$-shaped molecule

Identify the substance acting as an oxidant in the following reaction:
$BaCl_2 + Na_2SO_4 \to BaSO_4 + 2NaCl$

How many moles of $H_2SO_3$ are required to reduce one mole of $KMnO_4$ in an acidic medium?