Final answer:
Among the options listed, rubber is an example of an insulator because it does not easily allow the flow of electric charge, unlike the metals copper, aluminium, and gold, which are conductors.
Step-by-step explanation:
The question asks to identify an insulator from a list of materials. Insulators are materials that do not easily allow the flow of electric charge through them. Among the given options, copper, aluminium, and gold are all metals that are known to be good conductors, because they allow electric charges to move through them with relative ease. This is due to the loosely bound outer electrons in their atomic structure. In contrast, rubber is a material where the atoms and molecules hold on more tightly to their electrons, which makes it difficult for electric charge to move through it. Therefore, rubber is an example of an insulator and is the correct answer to this question.