Describe the role of
(i) NaCN in the extraction of gold from its ore.
(ii) Cryolite in the extraction of aluminium from pure alumina
(iii) CO in the purification of Nickel.

Explanation

(i) It helps in forming a soluble complex with gold and this process is known as leaching.
(ii) Cryolite lowers the high melting point of alumina and makes it a good conductor of electricity.
(iii)CO forms a volatite complex with Nickel metal which when heated decomposes to give pure nickel