What is an atom called when it has no free electrons?

An atom that has no free electrons is referred to as an insulator. In materials classified as insulators, the electrons are tightly bound to their respective atoms and are not free to move throughout the material. This lack of free charge carriers means that insulators do not conduct electricity effectively.

In contrast, conductors have free electrons that can move easily, allowing electric current to flow. Semiconductors, on the other hand, can conduct electricity under specific conditions when energy is supplied, such as through doping or applying an electric field. Superconductors are materials that can conduct electricity without resistance at very low temperatures, which involves a different mechanism than simple electron mobility.

Thus, an atom with no free electrons aligns with the characteristics of insulators, making it the correct identification.