The purest form of iron which contains only about 0.1% carbon is

Analysis

The question asks for the purest form of iron among the given options, specifically identifying the one with a very low carbon content (approximately 0.1%).

Concept Explanation

Iron is extracted from its ores and processed into different forms based on the amount of carbon and other impurities present. The properties of iron change significantly depending on its carbon content:

• Pig Iron: This is the crude form of iron obtained directly from the blast furnace. It contains about 3% to 5% carbon, along with other impurities like silicon, sulfur, and phosphorus. It is brittle and hard.
• Wrought Iron: This is the purest form of commercial iron. It is produced by refining pig iron to remove almost all impurities. It contains less than 0.2% carbon (typically around 0.1%). Because of its high purity, it is malleable, ductile, and tough.
• Cast Iron: This is made by remelting pig iron with scrap iron and coke. It contains about 2% to 4% carbon. It is very hard but brittle.
• Iron Pyrite ($FeS_2$): This is an ore of iron, commonly known as "fool's gold." It is a mineral, not a processed form of metallic iron.

Step-by-Step Solution

1. Evaluate Pig Iron: Contains 3–5% carbon. This is high, so it is not the purest form.
2. Evaluate Wrought Iron: Contains approximately 0.1% carbon. This matches the description in the question perfectly.
3. Evaluate Cast Iron: Contains 2–4% carbon. This is too high to be considered the purest form.
4. Evaluate Iron Pyrite: This is a chemical compound (sulfide ore), not a metallic form of iron used in industry.

Comparing these, wrought iron is the form that contains the least amount of carbon, making it the purest form of iron listed.

Conclusion

Exam Tip: Remember the "Carbon Rule": The higher the carbon content, the harder and more brittle the iron. The lower the carbon content, the softer, more malleable, and purer the iron. Wrought iron is the "purest" and "softest" of the three main industrial types.