Which cell will measure standard electrode potential of copper electrode?

Electrode potential for Mg electrode varies according to the equation

${\mathrm{E}}_{{\mathrm{Mg}}^{2+}/\mathrm{Mg}}={\mathrm{E}}_{{\mathrm{Mg}}^{2+}/\mathrm{Mg}}^{\mathrm{\Theta }}-\frac{0.059}{2}\log \frac{1}{\left[{\mathrm{Mg}}^{2+}\right]}$

The graph of ${\mathrm{E}}_{{\mathrm{Mg}}^{2+}/\mathrm{Mg}}$ vs $\log \left[{\mathrm{Mg}}^{2+}\right]$ is

Using the data given below find out the strongest reducing agent.

${\mathrm{E}}_{{\mathrm{Cr}}_2{\mathrm{O}}_7^{2-}/{\mathrm{Cr}}^{3+}}^{\mathrm{\Theta }}=1.33 \mathrm{V} {\mathrm{E}}_{{\mathrm{Cl}}_2/{\mathrm{Cl}}^{-}}^{\mathrm{\Theta }}=1.36 \mathrm{V}$

${\mathrm{E}}_{{\mathrm{MnO}}_4^{-}{\mathrm{Mn}}^{2+}}^{\Theta }=1.51 \mathrm{V} {\mathrm{E}}_{{\mathrm{Cr}}^{3+}/\mathrm{Cr}}^{\Theta }=-0.74 \mathrm{V}$

${\mathrm{E}}_{{\mathrm{Cr}}_2{\mathrm{O}}_7^{2-}/{\mathrm{Cr}}^{3+}}^{\mathrm{\Theta }}=1.33, \mathrm{V} {\mathrm{E}}_{{\mathrm{Cl}}_2/{\mathrm{Cl}}^{-}}^{\mathrm{\Theta }}=1.36 \mathrm{V}$, ${\mathrm{E}}_{{\mathrm{MnO}}_4^{-}/{\mathrm{Mn}}^{2+}}^{\Theta }=1.51, \mathrm{V} {\mathrm{E}}_{{\mathrm{Cr}}^{3+}/\mathrm{Cr}}^{\Theta }=-0.74 \mathrm{V}$