Charging by friction transfers electrons

Steps:

• Rubbing transfers electrons between materials based on their electron affinity.
• Plastic has higher electron affinity than cloth, so it gains electrons.
• Gaining electrons makes the plastic negatively charged.
• The cloth loses electrons and becomes positively charged.

Why B is correct:

• Negative charge results from gaining electrons, as defined by atomic structure where electrons carry negative charge.

Why the others are wrong:

• A: Earth grounding isn't involved in simple rubbing; charge comes from the cloth.
• C: Electrons don't move within the cloth to the plastic; transfer is direct between surfaces.
• D: Protons are bound in nuclei and not transferred in friction.

Final answer: B