How many electrons are involved in the reduction of $KMnO_4$ in a basic medium?

Assign $A, B, C, D$ from the given type of reaction.
$3PbS + 8HNO_3 \text{ (dil.)} \longrightarrow 3Pb(NO_3)_2 + 3S \downarrow + 2NO + 4H_2O$

How many moles of $K_2Cr_2O_7$ can be reduced by $1 \ mol$ of $Sn^{2+}$?

The equivalent weight of $KIO_3$ in the reaction $2Cr(OH)_3 + 4OH^{-} + KIO_3 \to 2CrO_4^{2-} + 5H_2O + KI$ is

On balancing the given redox reaction,$aCr_2O_7^{2-} + bSO_3^{2-}{(aq)} + cH^{+}{(aq)}$ $\rightarrow 2aCr^{3+}{(aq)} + bSO_4^{2-}{(aq)} + \frac{c}{2}H_2O_{(l)}$,the coefficients $a$,$b$,and $c$ are found to be,respectively-

What is the number of moles of electrons gained by one mole of oxidizing agent in the following redox reaction?
$Zn_{(s)} + 2HCl_{(aq)} \longrightarrow ZnCl_2(aq) + H_2(g)$