Which of the following materials is not commonly used for electrical conductors?

Plastic is not commonly used for electrical conductors because it is an insulator rather than a conductor of electricity. Conductive materials allow electric current to flow through them easily, while insulating materials, like plastic, are characterized by their high resistance to electrical flow.

Copper and aluminum are widely used as conductors in electrical systems due to their excellent conductivity and malleability. Steel, while primarily used in construction due to its strength, can also be used as a conductor, particularly in specific applications such as power transmission lines, although it is often used in combination with other conductive materials. In contrast, plastic serves the vital role of insulating electrical conductors, protecting users from electric shock and preventing short circuits between conductive elements.