Aluminium extraction from its ore​

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. The ions in the aluminium oxide must be free to move so that electricity can pass through it. Aluminium oxide has a very high melting point (over 2000°C) so it would be expensive to melt it. Aluminium oxide does not dissolve in water, but it does dissolve in molten cryolite. This is an aluminium compound with a lower melting point than aluminium oxide. The use of cryolite reduces some of the energy costs involved in extracting aluminium.

Ibelieve its a because an empirical formula usually has a ch in it your options are a or b