61. (i) Write three balanced equations for the purification of bauxite by Hall's process.   62. (ii) Name a chemical used for dissolving aluminium oxide. In which state of sub-division is the chemical used?   63. (iii) Write an equation for the reaction which takes place at the anode during the extraction of aluminium by the electrolytic process.   64. (iv) Mention one reason for the use of aluminium in thermite welding.