Which of the following is a good electrical insulator?

An electrical insulator is a material that strongly opposes the flow of electric current. This happens because the electrons in insulating materials are tightly bound to their atoms, leaving very few free electrons available to carry a charge. Glass is a classic example of an excellent insulator and is frequently used in high-voltage applications and antique radio antennas. The other options provided are all conductors. Sea water contains dissolved salts (ions) that allow electricity to flow easily. Stainless steel is a metal and inherently conductive, while graphite (a form of carbon) is also a known electrical conductor.