Why aluminium can be used as a reducing agent for the reduction of chronic oxide?

Explanation

Ellingham diagram is used to predict thermodynamic feasibility of reduction of oxides of one metal by another metal.Any metal can reduce the oxides of other metals that ar located above it in the diagram .for example ,in the Ellingham diagram ,for the formation of chromium oxide lies above that of the aluminium,meaning that `Al_(2)O_(3)` is more stable than`Cr_(2)O_(3)`.Hence aluminium can be used as a reducing agent for the reduction of chromic oxide.However ,it cannot be used to redice the oxides of magnesium and calcium which occupy lower position than aluminium oxide.