Final answer:
The left conducting plate remains negatively charged and the right plate remains positively charged, making the correct answer D: Negative on the left plate and positive on the right plate.
Step-by-step explanation:
When two conducting plates are charged and placed close together, the resulting charge distribution is influenced by their respective charges. Given that the left plate is negatively charged and the right plate has twice as much positive charge, electrons on the left plate will be attracted towards the positively charged right plate. However, since electrical neutrality must be maintained overall, the excess charge remains on each plate respectively. Therefore, the left plate will be negatively charged and the right plate will be positively charged, resulting in answer D: Negative on the left plate and positive on the right plate.