The free energy of formation $(\Delta_f G^{\circ})$ of CO from C becomes lowerat temperatures above 1120 K whereas that of $\mathrm{CO}_2$ from C becomes lowerabove 1323 K than $(\Delta_f G^{\circ})$ of ZnO. However, $(\Delta_f G^{\circ})$ of $\mathrm{CO}_2$ from CO is alwayshigher than that of ZnO. Therefore, C can reduce ZnO to Zn but not CO.Therefore, out of C and CO, C is a better reducing agent than CO forZnO.Reduction of Zn is usually carried out around 1673 K, $\mathrm{ZnO} + \mathrm{C} \xrightarrow{1673\,\text{K}} \mathrm{Zn} + \mathrm{CO}$