Which of the following is classified as a ferrous metal?

Cast iron is classified as a ferrous metal because it contains a significant amount of iron, typically over 2% by weight. Ferrous metals are those that have iron as a primary component. This classification includes various alloys and forms of iron, such as cast iron, which is used widely in plumbing for pipes, fittings, and fixtures due to its durable nature and excellent fluid retention properties.

The other options represent non-ferrous metals. Aluminium is lightweight, has good corrosion resistance, and is often used in applications where weight is a factor, but it lacks iron. Copper is known for its electrical conductivity and is also resistant to corrosion, primarily used in plumbing for piping and fittings, but it does not contain iron. Brass, an alloy of copper and zinc, is frequently used for plumbing fixtures due to its machinability and acoustic properties, but it also lacks iron. Understanding these classifications is crucial in plumbing, as they dictate the suitability of materials for various applications based on their properties.