\[
\begin{array}{|c|c|c|}
\hline \text{reaction} & \text{reactants oxidized} & \text{reactants reduced} \\
\hline \mathrm{O}_{2}(\mathrm{~g}) + 2 \mathrm{Cu}(s) \rightarrow 2 \mathrm{CuO}(s) & \boxed{\mathrm{Cu}} & \boxed{\mathrm{O}_2} \\
\hline 8 \mathrm{Ni}(s) + \mathrm{S}_{8}(s) \rightarrow 8 \mathrm{NiS}(s) & \boxed{\mathrm{Ni}} & \boxed{\mathrm{S}_8} \\
\hline \mathrm{Cr}(s) + 2 \mathrm{Cl}_{2}(\mathrm{~g}) \rightarrow \mathrm{CrCl}_{4}(s) & \boxed{\mathrm{Cr}} & \boxed{\mathrm{Cl}_2} \\
\hline
\end{array}
\]