Which of the following materials is NOT considered a good conductor of electricity?

Rubber is not considered a good conductor of electricity; in fact, it is known as an insulator. Insulating materials like rubber have high resistance to the flow of electric current, which makes them effective in preventing the unintended flow of electricity. This property is crucial in electrical applications, where insulators are used to protect individuals and equipment from electric shock and to contain the current within conductors.

On the other hand, materials like copper, silver, and aluminum are excellent conductors of electricity due to their structure, which allows electrons to flow freely. These metals are commonly used in electrical wiring and components because they promote efficient electrical conduction. Thus, the distinction is clear: while copper, silver, and aluminum facilitate the flow of electricity, rubber serves as a barrier to it, making it an effective insulator.