Which of the following is classified as a ferrous pipe?

Ferrous pipes are those that contain iron, which makes them susceptible to rust and corrosion but also provides strength and durability. Iron is a primary metal used in the production of various types of piping due to its strength and structural integrity. Pipes made of iron or steel (which is an alloy that primarily consists of iron) are often used in construction and plumbing applications.

In contrast, brass is an alloy of copper and zinc, while copper itself is a non-ferrous metal that does not contain iron. Lead, although it is a heavy metal, also does not contain iron and is classified separately from ferrous materials. Thus, among the options provided, iron is the only material that fits the classification of a ferrous pipe due to its iron content.