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

In the thermal decomposition of a metal carbonate,the oxidation state of the metal changes if the metal is

The total change in the oxidation state of manganese involved in the reaction of $KMnO_4$ and potassium iodide in the acidic medium is $..........$.

See the following chemical reaction:
$Cr_2O_7^{2-} + XH^{+} + 6Fe^{2+} \rightarrow YCr^{3+} + 6Fe^{3+} + ZH_2O$
The sum of $X$,$Y$ and $Z$ 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-

Which of the following reactions involves oxidation-reduction?