Hint: Iron exists in its mineral form on earth’s crust. The purest form of iron was used to make swords in the olden times. It was also used to build iron gates, utensils etc.
> The purest form of iron is Wrought iron. It is an alloy of iron with very low carbon content when compared with cast iron. It is a semi-fused mass of iron which has fibrous slag inclusions. Wrought iron is tough, malleable, ductile and can be easily welded.
> Before steel, wrought iron was considered as the most malleable iron. The name wrought is given to it because it can be hammered, rolled or when hot enough can expel molten slag. Modern use of wrought iron is equivalent to mild steel which is also called low-carbon steel.
> Wrought iron is highly refined with very small amounts of slag forged into fibres. The silicate filaments of the slag protect the iron from corrosion and decrease the damages caused by shock and vibration.
> In olden days, wrought irons were used to make swords, cutlery, chisels, axes and other edged tools. Nowadays wrought iron is used to make nails, rivets, wire, chains, rails, railway couplings, water and steam pipes, nuts, bolts, and many other things.
> Wrought iron is no longer produced on a large scale now. Many of them are now replaced with mild steel. Thus, the purest form of iron is wrought iron.
So, the correct answer is (b).
Note: Cast iron is also another pure form of iron, but it consists of silicon, manganese and other traces of elements. But iron content in it is 2-4%. In case of wrought iron, Iron is made into a slag, there are no other elements in them.