In which reaction is nitrogen reduced? \mathrm{Cu}^{2+}+2 \mathrm{NO}_{2}+2 \mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{Cu}+4 \mathrm{H}^{+}+2 \mathrm{NO}_{3}^{-} \mathrm{Q} 4 \mathrm{Zn}+10 \mathrm{H}^{+}+\mathrm{NO}_{3}^{-} \rightarrow 4 \mathrm{Zn}^{2+}+\mathrm{NH}_{4}{ }^{+}+3 \mathrm{H}_{2} \mathrm{O} 2 \mathrm{NO}+\mathrm{O}_{2} \rightarrow 2 \mathrm{NO}_{2} 4

\mathrm{NH}_{3}+5 \mathrm{O}_{2} \rightarrow 4 \mathrm{NO}+6 \mathrm{H}_{2} \mathrm{O}