Which of the following materials is magnetic?

Cobalt is considered a magnetic material because it exhibits ferromagnetism, which means it can be magnetized and attracted to a magnet. This property is due to the alignment of electron spins in cobalt atoms, allowing it to maintain a magnetic field even when the external magnetic influence is removed. Cobalt is widely used in various applications, including the production of strong permanent magnets and magnetic alloys, making it an essential element in the field of magnetism.

In contrast, copper and gold are not magnetic materials; they do not have ferromagnetic properties and cannot be magnetized. Instead, these metals are better known for their excellent electrical conductivity. Plastic is also non-magnetic, as it is composed of synthetic or natural polymers that do not possess the properties needed to interact with magnetic fields. Therefore, cobalt stands out as the only one among the options provided that demonstrates true magnetic characteristics.