Степень окисления и ОВР

$\mathrm{А}) {\mathrm{NH}}_3 + {\mathrm{O}}_2 \to \mathrm{NO} + {\mathrm{H}}_2\mathrm{O}$
$\mathrm{Б}) \mathrm{Fe} + {\mathrm{KNO}}_3 + \mathrm{KOH} \to {\mathrm{KFeO}}_{2 }+ {\mathrm{N}}_2 + {\mathrm{H}}_2\mathrm{O}$
$\mathrm{В}) {\mathrm{Fe}}_2{\left({\mathrm{SO}}_4\right)}_3 + {\mathrm{SO}}_2 + {\mathrm{H}}_2\mathrm{O} \to {\mathrm{FeSO}}_4 + {\mathrm{H}}_2{\mathrm{SO}}_4$

^{$1) {\mathrm{Э}}^0 \to {\mathrm{Э}}^{-2}$}
$2) {\mathrm{Э}}^{+4} \to {\mathrm{Э}}^{+6}$
$3) {\mathrm{Э}}^{+5} \to {\mathrm{Э}}^0$
$4) {\mathrm{Э}}^0 \to {\mathrm{Э}}^{+3}$
$5) {\mathrm{Э}}^{-3}\to {\mathrm{Э}}^{+2}$