Question

The purest common form of iron is:

• A. Pig iron
• B. Cast iron
• C. Wrought iron
• D. None of the above

Hint:

Compare carbon content, less carbon and fewer impurities means a purer form of iron.

Answer 1

The Correct Option is C

Rank the iron types by how much carbon and impurity they retain, since lower carbon content means higher purity for iron.
Option A, pig iron: this is the raw output straight from the blast furnace, loaded with roughly 3 to 4.5 percent carbon plus silicon, sulfur and phosphorus impurities, making it the most impure and most brittle of all the iron grades, definitely not the purest.
Option B, cast iron: made by remelting pig iron, this still holds a substantial 2 to 4 percent carbon, giving it a low melting point good for casting into moulds but also real brittleness, so it remains far from pure.
Option C, wrought iron: produced through the puddling process, where molten iron is churned with iron oxide to burn off carbon and other impurities as slag, the final carbon content drops below about 0.5 percent, with the small remaining slag giving it a fibrous, tough, corrosion resistant structure. Of the three common industrial forms, this has by far the least carbon and the fewest impurities, making it the purest common form of iron.
Option D, none of the above: this cannot be right, because wrought iron in option C genuinely fits the description of the purest common iron, so there is no need to reject all three.
By carbon content and purity, wrought iron clearly wins, confirming option C as the correct answer.