Which of the following is a famous hill station that, historically, belonged to the Indian state of Uttar Pradesh?

Introduction / Context:
This question is about Indian tourism and political geography. It asks which hill station was associated with Uttar Pradesh, keeping in mind that state boundaries have changed over time. Nainital is an important hill station that used to belong to Uttar Pradesh before the creation of the separate state of Uttarakhand.

Given Data / Assumptions:
- The options list well known hill stations: Darjeeling, Dalhousie, Kulu, Nainital and Mount Abu.
- The question mentions Uttar Pradesh as the reference state, historically speaking.
- It assumes familiarity with the reorganisation that created Uttarakhand from the hill districts of Uttar Pradesh in the year 2000.

Concept / Approach:
Nainital is located in the Kumaon region of the Himalayas. Before the formation of Uttarakhand in 2000, this region was part of Uttar Pradesh, and Nainital was one of the prominent hill stations of that state. Darjeeling is in West Bengal, Dalhousie in Himachal Pradesh, Kulu (Kullu) also in Himachal Pradesh and Mount Abu in Rajasthan. Therefore, the only hill station that can correctly be described as having belonged to Uttar Pradesh is Nainital.

Step-by-Step Solution:
Step 1: Recall that Uttarakhand was carved out of Uttar Pradesh in 2000, taking with it the hill districts including Nainital.Step 2: Nainital was historically listed as a hill station of Uttar Pradesh in older textbooks and government records.Step 3: Identify the present locations of the other hill stations: Darjeeling in West Bengal, Dalhousie and Kullu in Himachal Pradesh and Mount Abu in Rajasthan.Step 4: None of these other hill stations were ever part of Uttar Pradesh.Step 5: Therefore, Nainital is the only option that fits the description of a hill station in Uttar Pradesh (historically).

Verification / Alternative check:
Older administrative maps of India from before 2000 show Nainital district within the boundaries of Uttar Pradesh. The creation of Uttarakhand shifted Nainital into the new hill state, but exam questions often preserve the earlier association. Tourism literature that references "UP hill stations" from that period typically mentions Nainital, Mussoorie and other locations that are now in Uttarakhand.

Why Other Options Are Wrong:
Darjeeling: Located in the state of West Bengal and has never been part of Uttar Pradesh.

Dalhousie: Located in Himachal Pradesh in the western Himalayas.
Kulu (Kullu): Also in Himachal Pradesh, known for its valley and proximity to Manali.
Mount Abu: The only hill station of Rajasthan, located in the Aravalli Range, not associated with Uttar Pradesh.

Common Pitfalls:
Some candidates may ignore the hint about Uttar Pradesh and simply focus on well-known hill stations like Darjeeling or Dalhousie. Others may not be aware of the historical change in boundaries when Uttarakhand was created. Remembering that Nainital and other Kumaon and Garhwal hill stations once belonged to Uttar Pradesh is essential for correctly answering such questions.

Final Answer:
Nainital