C Give two reasons why the formation of aluminium by electrolysis is very
expensive:

It is expensive, largely because of the amount of electricity required in the extraction process. Aluminium ore is called bauxite . The bauxite is purified to produce aluminium oxide, a white powder from which aluminium can be extracted. The extraction is done by electrolysis.

a compound is a molecule made of atoms from different elements.

a. by the combination of an unlimited number of elements