Final Answer:
Statement II and III in the prompt are key to explaining why the plate at the top of the electroscope contains negative charges. Thus, the correct option is d).
Step-by-step explanation:
The key statements in the prompt that explain why the plate at the top of the electroscope contains negative charges are II and III. Statement II suggests that the electroscope initially has a neutral charge, and statement III indicates that a negatively charged rod is brought near the metal cap of the electroscope. These two statements collectively explain the process: when the negatively charged rod is brought close, it induces a separation of charges, causing the electrons to move towards the top plate of the electroscope, leaving it with a net negative charge.
Statement II establishes the baseline of a neutral electroscope, while statement III introduces the external influence of the negatively charged rod. As the negatively charged rod approaches the neutral electroscope, it repels electrons in the metal cap, forcing them to move to the top plate. This movement of electrons creates an excess of negative charges on the top plate, resulting in an overall negative charge on the electroscope. Understanding these statements is crucial for comprehending the process of charge induction and distribution on an electroscope in response to an external charge.
In summary, statements II and III work in conjunction to explain why the plate at the top of the electroscope contains negative charges. They provide the necessary information to grasp the fundamental principles of charge distribution and induction in an electroscope when influenced by an external charged object.