Which type of steel is categorized based on the percentage of carbon in the alloy?

The categorization of steel based on the percentage of carbon present in the alloy is accurately represented by carbon steel. This type of steel primarily consists of iron and carbon, with the carbon content typically ranging from approximately 0.05% to 2.0%. The different levels of carbon significantly influence the properties and applications of the steel. For instance, lower carbon content results in higher ductility and malleability, whereas higher carbon content enhances hardness and strength, making carbon steel versatile for various applications.

In contrast, alloy steel incorporates additional alloying elements such as chromium, nickel, and manganese to enhance specific properties beyond carbon content alone. Stainless steel, defined by its resistance to corrosion and oxidation, generally contains a minimum of 10.5% chromium, and its categorization doesn't primarily focus on carbon percentage. Mild steel, typically a subset of carbon steel with a low carbon content, is defined for its specific applications and characteristics but does not represent the broader classification of all carbon steels.

Thus, carbon steel is the correct choice as it directly relates to the classification of steel based on the carbon percentage in the alloy.