Which of the following is NOT a type of alloy?

Iron is considered a pure element and not an alloy, making it the correct answer to this question. An alloy is typically a combination of two or more metals, or a metal with non-metal elements, that results in improved properties such as strength, ductility, or resistance to corrosion.

Brass, stainless steel, and bronze are all well-known alloys; brass is a mixture of copper and zinc, stainless steel combines iron with chromium (and sometimes nickel), and bronze is primarily made of copper and tin. Each of these alloys possesses unique characteristics that stem from their specific combinations of metals, showcasing the advantages of alloying in metallurgical applications.

Understanding the distinct composition of these materials is crucial for various engineering and manufacturing practices, especially when selecting materials for projects that require specific mechanical properties or corrosion resistance.