The reducing agent in the given equations: $4 \, Ag_{(s)} + 8 \, CN_{(aq)}^{-} + 2 \, H_2O_{(l)} + O_{2(g)} \rightarrow 4 \left[ Ag(CN)_2 \right]_{(aq)}^{-} + 4 \, OH_{(aq)}^{-} \\ 2 \left[ Ag(CN)_2 \right]_{(aq)}^{-} + Zn_{(s)} \rightarrow \left[ Zn(CN)_4 \right]_{(aq)}^{2-} + 2 \, Ag_{(s)}$