Suggest a condition under which magnesium could reduce alumina. The two equations are :
(a) `4/3Al + O_2 to 2/3 Al_2O_3`
(b) `2Mg + O_2 to 2MgO`

Explanation

At the point of intersection of the `Al_2O_3` and Mgo curves (marked "A" in Ellingham diagram), the `A,G^(Theta)` becomes ZERO for the reaction:
`2/3Al_2O_3 + 2Mg to 2MgO + 4/3 Al`
- Below that point magnesium can reduce alumina.