To answer this question, the user needs to be familiar with the popular luxury trains of India and their respective routes.
Option A: Palace on Wheels - This luxury train was indeed originally meant to be used by the rulers of the erstwhile states of Rajputana, Gujarat and the Nizam of Hyderabad and the Viceroy of British India. It departs from New Delhi on an 8 day journey covering the states of Rajasthan and Uttar Pradesh. Therefore, this option is correct.
Option B: Thar Express - Thar Express is a weekly international train that runs between India and Pakistan connecting Jodhpur in Rajasthan to Karachi in Pakistan. This option is incorrect as Thar Express does not operate on the given route.
Option C: Hussainsagar Express - Hussainsagar Express is a daily express train that runs between Mumbai and Secunderabad in Telangana. This option is incorrect as this train does not operate on the given route.
Option D: Deccan Queen - Deccan Queen is a daily high-speed train that runs between Mumbai and Pune in Maharashtra. This option is incorrect as this train does not operate on the given route.
Therefore, the answer is: A. Palace on Wheels.