Which of the following metal oxide is more stable if the free energies of formation of ${\mathrm{Cr}}_2{\mathrm{O}}_3,$ and ${\mathrm{Al}}_2{\mathrm{O}}_3$ per mole of oxygen consumed are -540 kJ and -827 kJ respectively?

Aluminium oxide is stable if the free energies of the formation of  ${\mathrm{Cr}}_2{\mathrm{O}}_3,$and ${\mathrm{Al}}_2{\mathrm{O}}_8$ per mole of oxygen consumed are -540 kJ and -827 kJ respectively.

According to the Ellingham diagram, a metal's stability in the form of its oxide increases with the location of the metal line; the lower the metal line, the more negative the Gibbs free energy, and the more stable the metal will be.

Hence the correct option is B