Which of the following is an example of a ferromagnetic material?

Ferromagnetic materials are those that can be magnetized and have high magnetic permeability, meaning they can be easily magnetized and retain their magnetic properties. Iron is a classic example of a ferromagnetic material due to its ability to be magnetized and its significant magnetic strength. It possesses a crystalline structure that allows for the alignment of magnetic domains, which contributes to its ferromagnetic properties.

In contrast, aluminum, copper, and gold are not ferromagnetic. Aluminum is paramagnetic, meaning it has a very weak magnetic response and does not retain magnetization. Copper is also not magnetic in any substantial way, as it is a diamagnetic material, which means it is repelled by magnetic fields. Gold, while it has some interesting electrical properties, is likewise a diamagnetic material, showing no significant magnetic properties. Therefore, iron stands out as the sole ferromagnetic material among the options provided.