Which of the following is NOT a type of insulator?

Copper is not considered a type of insulator; rather, it is a well-known conductor of electricity. Conductors are materials that allow electric current to flow through them easily due to their free electrons. In contrast, insulators are materials that resist the flow of electric current, preventing it from passing through.

Glass, rubber, and wood are all effective insulators. They have tightly bound electrons, making it difficult for electric currents to pass through, which is why they are often used in electrical applications to protect against unintentional contact with live wires. This property helps to ensure safety when using electrical devices and systems.