a. Cast iron is formed by heating pig iron, scrap iron and coke. Cast iron contains about 3% of carbon. Cast iron expands on solidification. So these are used to make molds. Though it is strong, it is brittle.
b. When cast iron is purified, it becomes wrought iron which is comparatively a pure form of iron. Wrought iron contains about 0.2% to 0.5% of carbon. Small amounts of phosphorus, silicon, etc. are also present.