Which term describes a material that does not allow electrons to move easily?

• A. Electrical conductor
• B. Electrical insulator
• C. Semiconductor
• D. Resistor

Answer: (B)

The main idea is how well a material lets electrons move, which is about electrical conductivity. A material that does not allow electrons to move easily is an electrical insulator. Insulators have high resistance and very few free charge carriers at room temperature, so electrons stay basically in place. In terms of energy bands, the valence band is filled and the gap to the conduction band is large, so thermal energy isn’t enough to free electrons to conduct. This is why rubber, glass, and plastic are good insulators. The other concepts describe different ideas: a conductor lets electrons move freely; a semiconductor conducts under certain conditions and can be controlled; a resistor is a device used to limit current, not a material property.