State one relevant observation for the reaction : Sulphide ore is added to a tank containing oil and water and then stirred or agitated with air.

Give the chemical formula of :

(i) Bauxite

(ii) Cryolite

(iii) Sodium aluminate

Name the gas evolved when : Alumina undergoes electrolytic reduction.

Answer the following questions based on the extraction of aluminium from alumina by Hall- Heroult's Process.

(i) What is the function of cryolite used along with alumina as the electrolyte.

(ii) Why is the powdered coke sprinkled on top of the electrolyte.

(iii) Name the electrode from which aluminium is collected.