The correct answer is B. Lahaul and Spiti.
Lahaul and Spiti is a district in the Indian state of Himachal Pradesh. It is the least populous district in the state, with a population of just over 30,000 people. The district is located in the Himalayas, and its terrain is largely mountainous. The climate is cold and dry, and the district is sparsely populated.
The other options are incorrect because they are all more populous than Lahaul and Spiti. Chamba has a population of over 500,000 people, Kullu has a population of over 400,000 people, and Kinnaur has a population of over 100,000 people.
Lahaul and Spiti is a beautiful and remote district, and it is a popular destination for tourists. The district is home to a number of monasteries, and it is also a good place for trekking and mountaineering.