What is a common example of an insulator?

Rubber is a common example of an insulator due to its properties that resist the flow of electrical current. Insulators are materials that do not easily allow the flow of electricity, providing a barrier that prevents unwanted electrical conduction. This characteristic makes rubber an ideal choice for insulation around electrical wires and components, ensuring safety and efficiency in various applications.

In contrast, materials like copper, aluminum, and gold are excellent conductors of electricity. They allow for easy flow of electrical current, which is why they are commonly used in electrical wiring and electronic devices. Therefore, rubber's insulating properties are what distinctly categorize it as the correct answer in this context, highlighting its role in providing safety and preventing electric shock or short circuits.