Which of the following is an example of a conductor?

• A. Rubber
• B. Glass
• C. Plastic
• D. Saltwater

Answer: (D)

This item tests whether a substance can conduct electric current. Conductors have mobile charge carriers that respond to an electric field, allowing current to flow easily. Saltwater is a conductor because the dissolved salts dissociate into ions that can migrate when voltage is applied; these ions carry charge through the solution and enable current. In contrast, rubber, glass, and plastic are insulators because their electrons are tightly bound and there are few free charge carriers, so these materials resist the flow of electricity. That’s why salts in water enable conduction while common plastics, rubber, and glass do not.