(a) (i) Rancidity can be prevented by adding antioxidants to food containing
fat and oil, e.g. butylated hydroxy anisole is added to butter as antioxidant.
(ii) It can be prevented by packaging fat and oil containing foods in nitrogen gas.
(b) (i) Molten NaCl is electrolytically decomposed to form sodium metal.
(ii) Aluminium metal is obtained by electric decomposition of bauxite ore mixed with cryolite.
(iii) Carbonate ores are thermally decomposed to give metal oxide which on reduction give metal.