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-

For the balanced redox reaction $aZn + b \, HNO_3 \to c \, Zn(NO_3)_2 + d \, NH_4NO_3 + 3H_2O$,the value of $b$ is:

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$MnO_2 + 2NaCl + 2H_2SO_4 \longrightarrow MnSO_4 + Na_2SO_4 + 2H_2O + Cl_2 \uparrow$

Balance the following redox reactions by the ion-electron method:
$(a)$ $MnO_4^-(aq) + I^{-}(aq) \rightarrow MnO_2(s) + I_2(s)$ (in basic medium)
$(b)$ $MnO_4^-(aq) + SO_2(g) \rightarrow Mn^{2+}(aq) + HSO_4^-(aq)$ (in acidic solution)
$(c)$ $H_2O_2(aq) + Fe^{2+}(aq) \rightarrow Fe^{3+}(aq) + H_2O(l)$ (in acidic solution)
$(d)$ $Cr_2O_7^{2-} + SO_2(g) \rightarrow Cr^{3+}(aq) + SO_4^{2-}(aq)$ (in acidic solution)

For the redox reaction $xP_4 + yHNO_3 \to H_3PO_4 + NO_2 + H_2O$,find the values of $x$ and $y$.

In which reaction is there a change in the oxidation state?