(a) What is the most important ore of aluminium ? What is its formula ?
(b) How aluminium extracted from the ore ?
(c) Why is alumina dissolved in molten cryolite before subjecting it to electrolysis ?

Explanation

(a) The most important ore of aluminium is bauxite. Its formula is `Al_(2)O_(3).2H_(2)O`
(b) The ore is concentrated by method of chemical separation called Baeyer.s method.
The pure alumina `(Al_(2)O_(3))` obtained is dissolved ini molten cryolite `(Na_(3)AlF_(6))` and then subjected to electrolysis.
(c) Alumina has high melting point and not a good conductor for electricity. On dissolving it in molten cryolite, the mixture has lower melting point and is a better conductor of electricity.