Which of the following is the chief ore of aluminium? 

Bauxite

The correct answer is option 2. Bauxite.

The primary source of aluminum is bauxite. Bauxite is made up of hydrated iron oxide and hydrated aluminum oxide and has the chemical formula Al₂O₃.2H₂O. An further source of aluminum is kaolinite, although it is less common than bauxite and requires more effort and money to extract the metal.