Insulators are substances that:

Insulators are substances that:

• A. Substances that allow electrons to move freely
• B. Substances that bend light
• C. Substances that dissolve in water
• D. Substances that do not allow electrons to move freely

Answer: (D)

Materials that resist the flow of electric current are insulators. In an insulator, electrons are tightly bound to atoms and there are very few free electrons available to move in response to an electric field. Because charge cannot easily drift, the material does not conduct electricity well. This is why insulators are used to coat or separate electrical wiring and devices to prevent unwanted current flow. The other ideas describe different properties: bending light concerns optical refraction, which isn’t about electrical conduction; dissolving in water is about solubility; and allowing electrons to move freely describes conductors, not insulators.

Materials that resist the flow of electric current are insulators. In an insulator, electrons are tightly bound to atoms and there are very few free electrons available to move in response to an electric field. Because charge cannot easily drift, the material does not conduct electricity well. This is why insulators are used to coat or separate electrical wiring and devices to prevent unwanted current flow.

The other ideas describe different properties: bending light concerns optical refraction, which isn’t about electrical conduction; dissolving in water is about solubility; and allowing electrons to move freely describes conductors, not insulators.