Which of the following is also a good electrical insulator?

Glass is recognized as a good electrical insulator due to its atomic structure, which does not allow free electrons to move easily. This property means that glass can effectively resist the flow of electric current, making it an ideal material for applications where insulation from electricity is necessary. In various scenarios, such as capacitor design and electrical wiring insulation, glass provides the needed barrier to prevent unwanted conduction.

In contrast, metals like nickel, silver, and iron have free-moving electrons that enable them to conduct electricity efficiently. These materials are excellent conductors, not insulators, and are typically used to create pathways for electric current rather than block it. This distinction is critical in understanding the materials' purposes in electrical and electronic contexts.