The Hall Héroult process is used to produce what?
The Hall-Héroult process is probably the most common method of smelting aluminium industrially.
Alumina (or Aluminium Oxide,
At the cathode:
At the anode:
As to why the alumina must be dissolved in cryolite rather than just aqueous
PS: natural cryolite is far too rare to be used for electrolysis, so a synthetic version is created from fluorite, a far more common material.