Considering Ellingham diagram, which of the following metals can be used to reduce alumina?

Concept:

Ellingham diagram - 

• It is used in the evaluation of metal oxides and metal sulfides.
• It is a plot between Gibbs free energy and temperature.
• Ellingham's diagram makes the process of choosing a reducing agent for the formation of metal oxides easy.
• As, ΔG^o = ΔH^o - TΔS^o
  • If  ΔG^o = -ve, reaction is spontaneous.
  • If  ΔGo = 0, condition of equillibrium.
  • If  ΔGo = +ve, reaction will be non-spontaneous.
• Thus, it is used to find the feasibility of the reduction of ore.

Explanation:

The Ellingham diagram is a plot between ΔGo and T as given - 

• As ΔGo value give the feasibility of a chemical reaction.
• The more negative the ΔGo value, the more feasible the reaction is.
• In the given diagram, we can see that formation of aluminum oxide occur at ΔGo = ≈ -1050.
• Also, we can see that ΔGo value for MgO is ≈ -1100, the line for which lies exactly below the line for Alumina. The other metal oxides form at a less ΔGo value.
• As Mg has a more negative ΔGo value it has more tendency to form oxides.
• So, reacting Mg with alumina it has more chances to reduce alumina as Mg is more reactive than Al.

∴ the metal which is more reactive than 'Al' can reduce alumina is 'Mg'.

Hence, the correct answer is option 4.