Concept:Impurities in cast iron are removed by oxidation using haematite.Explanation:Cast iron is brittle due to impurities such as carbon, silicon, and phosphorus.It is heated in a furnace with haematite (Fe2O3).Oxygen from haematite oxidises the impurities and excess carbon, leaving behind relatively pure wrought iron.This process is called puddling.Answer:B. haematite.