Which of the following is considered a "brittle" metal?

Cast iron is considered a "brittle" metal due to its carbon content and the way its microstructure is arranged. When subjected to stress, cast iron tends to fracture rather than deform, which is characteristic of brittle materials. This brittleness makes it unsuitable for applications that require flexibility or tensile strength but ideal for others like pipes or heavy machinery components where compressive strength is more critical.

Other metals listed exhibit different properties; for instance, steel is known for its toughness and ductility, which allow it to bend and absorb energy without breaking. Gold is a very malleable and ductile metal, allowing it to be shaped easily without cracking. Aluminum also has good ductility and is commonly used in applications that require both structural integrity and lightweight materials.