Which of the following is also a good electrical insulator?

Glass is known for its excellent electrical insulating properties, making it a suitable material for applications where the prevention of electrical conduction is essential. It is an amorphous solid that does not allow the flow of electric current under normal conditions, thanks to its lack of free-moving charge carriers. This characteristic is crucial in various electrical and electronic devices where insulation from conductive materials is necessary to protect circuits and users from electric shock.

In contrast, the other materials listed are metals and have good electrical conductivity. Nickel, silver, and iron are all conductive materials, which means they allow the flow of electric current. Silver, in particular, is one of the best conductors of electricity, while nickel and iron are often used in applications where conductivity is required. Therefore, glass stands out as the appropriate choice for an electrical insulator.