Which of these materials is not considered a good conductor?

Rubber is considered an insulator rather than a conductor of electricity. Conductors are materials that allow the flow of electric current due to the presence of free electrons, and they typically have low resistance. In contrast, rubber has high resistance and does not facilitate the movement of electric current, making it a poor conductor.

Copper, aluminum, and gold are all excellent conductors. Copper is widely used in electrical wiring due to its excellent conductivity and flexibility. Aluminum, while less conductive than copper, is often used in overhead power lines because of its lightweight and cost-effectiveness. Gold is also a good conductor and is often used in high-performance electrical connections due to its resistance to corrosion, though it is not used as commonly as copper or aluminum in power transmission.