The fur gives up protons to the rod. The rod gives up electrons to the air. The fur gains protons from the rod. The rod gains electrons from the fur.
I gave my students this multiple choice question: Why does a plastic rod have a negative charge after being rubbed with a piece of fur?

Only one answer is correct among these 4 choices:
- The fur gives up protons to the rod.
- The rod gives up electrons to the air.
- The fur gains protons from the rod.
- The rod gains electrons from the fur.

Could you tell me which one is correct?

The rod gains electrons from the fur.