Which of the given metals cannot be extracted using smelting?

Smelting is a process of extracting impure metal from its ore at a high temperature in an enclosed furnace using a suitable flux (any substance introduced in the smelting of ores to promote fluidity and to remove impurities in the form of slag)and a reducing agent.

Aluminium cannot be extracted by the smelting process because :

• Aluminium is a highly electropositive element and has a strong affinity for oxygen. Hence, Al₂O₃ is a very stable compound and is not reduced by carbon.
• Al₂O₃ on heating with carbon forms aluminium carbide (Al₄C₃).