Which of the following materials is considered a good electric insulator?

Rubber is recognized as a good electric insulator due to its molecular structure, which does not allow electrons to flow freely. In insulators, the electrons are tightly bound to their respective atoms, preventing the conduction of electricity. This property makes rubber an ideal material for insulating electrical wires and devices, ensuring safety by minimizing the risk of electric shocks.

In contrast, materials like aluminum, copper, and gold are conductors, meaning they allow electricity to flow through them easily. Conductors have loosely bound electrons that can move freely, facilitating the transfer of electric current. Hence, when considering materials used for insulation, rubber stands out as the most effective choice. Its ability to withstand electrical currents while providing safety makes it invaluable in various applications in the field of electronics and electrical engineering.