The free energy formation ( Δ_fG^o ) of CO from C becomes lower at temperatures above 1120K whereas that of CO₂ from C becomes lower above 1323K than Δ_fG⁰ of ZnO. However, Δ _fG⁰ of CO₂ from CO is always higher 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 for ZnO.