The Gibbs energy for the decomposition of ${\mathrm{Al}}_2{\mathrm{O}}_3$ at 500⁰ C is as follows $\frac{2}{3}{\mathrm{Al}}_2{\mathrm{O}}_3⟶\frac{4}{3}\mathrm{Al}+{\mathrm{O}}_2;{\mathrm{\Delta }}_{\mathrm{r}}\mathrm{G}=+960\mathrm{kJ}$ The voltage needed for the electrolytic reduction of aluminium oxide $\left({\mathrm{Al}}_2{\mathrm{O}}_3\right)$ at 500⁰ C is at least