A part of Ellingham diagram is shown below :
(i) Will `Cr_2 O_3` be reduced by Al or not ?
(ii) Suggest a condition under which magnesium could reduced aluminium.

Explanation

(i) Since the `DeltaG` vs T curve for `Cr_2 O_3` lies above Al curve, Al can reduce `Cr_2 O_3`.
(ii) At the point of intersection of `Al_2 O_3` and MgO curves, `DeltaG` becomes zero for the reaction :
`2/3 Al_2 O_3 + 2Mg to 2MgO + 4/3 Al`
Therefore, below this point, the curve of magnesium lies below the curve for Al. Hence below this point, magnesium can reduce `Al_2 O_3` to Al.