The purest form of commercial iron is:

Iron obtained from its ores always contains some percentage of carbon and other impurities such as silicon, phosphorus, sulphur, etc. The various commercial forms of iron differ mainly in the amount of these impurities present.

We have the first variety, pig iron. It contains roughly $$3\% - 4\%$$ carbon along with appreciable amounts of silicon, phosphorus and sulphur. Because of such a high impurity content, pig iron is the crudest form and certainly not the purest.

Next comes cast iron. Cast iron is produced by remelting pig iron along with scrap iron and coke. Although the remelting removes a little carbon, cast iron still carries about $$2\% - 3\%$$ carbon and other impurities. Therefore, it is purer than pig iron but still far from being the purest.

Now consider wrought iron, sometimes called malleable iron. Wrought iron is prepared by oxidising molten pig iron in a reverberatory furnace lined with haematite. During this refining process most of the carbon, silicon, phosphorus and sulphur are oxidised away as their respective oxides and are removed in the slag. Because of this thorough oxidation, the final product contains only about $$0.1\% - 0.2\%$$ carbon and the total impurity content drops to a very low level. In terms of purity it attains nearly $$99.5\%$$ iron, making it the cleanest commercial form.

Finally, the combination “scrap iron and pig iron” is not a distinct refined form; it is merely a mixture used as a feed in some furnaces and therefore cannot qualify as a purer variety.

Comparing all four options, wrought iron clearly possesses the least percentage of carbon and other impurities and is therefore the purest form of commercial iron.

Hence, the correct answer is Option B.