Charging by friction transfers electrons

Steps:

• Rubbing the plastic rod with cloth causes friction, leading to charge transfer.
• The cloth becomes negatively charged, indicating it gains negative charge carriers.
• Negative charge carriers are electrons, which are mobile in such interactions.
• Thus, electrons move from the rod to the cloth, leaving the rod positively charged.

Why A is correct:

• Electrons are the primary mobile charge carriers in insulators like plastic; their transfer to the cloth explains the negative charge gained, per the law of conservation of charge.

Why the others are wrong:

• B: Protons are bound in nuclei and do not move between objects during friction.
• C: Electron movement from cloth to rod would make the cloth positively charged, contradicting the given information.
• D: Protons do not transfer in solids, and this would incorrectly charge the rod negatively.

Final answer: A