Wrought Iron: The Iron with the Least Percentage of Carbon
Wrought iron is the correct answer as it contains the least percentage of carbon among the options provided. Let's explore the characteristics and composition of each option to understand why wrought iron has the least carbon content.

Malleable Iron:
Malleable iron is a type of cast iron that undergoes heat treatment to improve its ductility and toughness. It has a higher carbon content compared to wrought iron. Malleable iron typically contains about 2-4% carbon, along with other alloying elements such as silicon, manganese, and sulfur. The higher carbon content imparts strength and hardness to malleable iron, making it suitable for applications requiring these properties.

Pig Iron:
Pig iron is produced by smelting iron ore in a blast furnace. It is the intermediary product formed during the iron production process and contains a high carbon content. Pig iron usually contains around 3-4% carbon, along with impurities like silicon, sulfur, and phosphorus. Its high carbon content makes it brittle and unsuitable for most engineering applications.

Stainless Steel:
Stainless steel is an alloy primarily composed of iron, chromium, and nickel. While it contains a significant amount of iron, stainless steel has a much lower carbon content compared to malleable iron and pig iron. The carbon content in stainless steel can range from as low as 0.03% up to 1.2% depending on the specific grade. The addition of chromium and nickel provides stainless steel with excellent corrosion resistance and other desirable properties.

Wrought Iron:
Wrought iron is a pure form of iron that contains an extremely low carbon content. It is produced by refining pig iron in a puddling furnace, which removes impurities and excess carbon. Wrought iron typically has a carbon content of less than 0.08%, making it nearly pure iron. It also exhibits excellent ductility and malleability, making it suitable for applications such as decorative ironwork, fences, and gates.

Conclusion:
In conclusion, among the given options, wrought iron has the least percentage of carbon. It is nearly pure iron with a carbon content of less than 0.08%. Malleable iron, pig iron, and stainless steel all have higher carbon contents compared to wrought iron, making them distinct from wrought iron in terms of their composition and properties.