The correct answer is: C. Sirmaur
Chandertal Lake is a high-altitude lake located in the Sirmaur district of Himachal Pradesh, India. It is situated at an elevation of 4,300 meters (14,100 feet) above sea level, and is one of the most popular tourist destinations in the state. The lake is surrounded by snow-capped mountains, and its clear waters reflect the surrounding peaks. Chandertal Lake is a popular spot for trekking, camping, and fishing.
Option A: Una is a district in the Indian state of Himachal Pradesh. It is located in the central part of the state, and is bordered by the districts of Bilaspur, Hamirpur, Kangra, and Solan. The district has a population of over 1.2 million people, and its headquarters is the town of Una.
Option B: Chamba is a district in the Indian state of Himachal Pradesh. It is located in the western part of the state, and is bordered by the districts of Kangra, Kullu, Lahaul and Spiti, and Kinnaur. The district has a population of over 500,000 people, and its headquarters is the town of Chamba.
Option C: Sirmaur is a district in the Indian state of Himachal Pradesh. It is located in the southern part of the state, and is bordered by the districts of Solan, Shimla, Kullu, and Mandi. The district has a population of over 400,000 people, and its headquarters is the town of Nahan.
Option D: Lahaul and Spiti is a district in the Indian state of Himachal Pradesh. It is located in the eastern part of the state, and is bordered by the districts of Kinnaur, Chamba, and Kullu. The district has a population of over 30,000 people, and its headquarters is the town of Keylong.