(a) Carbonate ore: It produces CO2 with brisk effervescence.
(i) Calcination: Carbonate ore is heated in limited supply of air and oxide is obtained. It releases carbon dioxide as a colourless and odourless gas with brisk effervescence. Hence, by the calcination process the metal carbonate ore are converted to their metal oxides.
e.g. ZnCO3 → ZnO + CO2
(ii) Reduction with carbon: Oxide ore is heated with carbon ZnO (s) + C (s) → Zn (s) + CO (g)