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

Step 1: Iron obtained from its ores exists commercially in a few grades, and these grades differ mainly in how much carbon and other impurities they still contain, more impurity generally means more brittleness and less purity.
Step 2: Pig iron is the crude iron tapped directly from a blast furnace, it contains the highest amount of carbon, roughly 3 to 4.5 percent, plus impurities like silicon, sulfur, phosphorus and manganese, making it the most impure and brittle form, it cannot even be shaped by hammering. Cast iron is made by remelting pig iron with scrap and coke, it still carries a fairly high carbon content, about 2 to 4 percent, giving it good fluidity for moulding but real brittleness. Wrought iron, in contrast, is manufactured by a puddling process where molten pig iron is stirred and reacted with iron oxide, oxidising away most of the carbon and other impurities as slag, leaving a product with carbon content below about 0.5 percent along with a small amount of intermixed silicate slag. This very low carbon content is what gives wrought iron its purity, along with excellent malleability and ductility, it can be hammered and rolled into shape and resists corrosion better than the other two.
Step 3: Since pig iron and cast iron both retain much higher carbon percentages, they are clearly less pure than wrought iron, so options A and B are eliminated, and since wrought iron does correctly answer the question, option D, none of the above, is also ruled out.
Step 4: Therefore wrought iron, option C, is the purest common commercial form of iron.