Степень окисления и ОВР

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

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