The correct answer is (c), Chamoli. Chamoli is the largest district in Uttarakhand, with an area of 9,013 square kilometers. It is located in the Garhwal region of the state. The district is home to the Nanda Devi National Park, which is a UNESCO World Heritage Site. Chamoli is also home to the Kedarnath Temple, which is one of the most important Hindu pilgrimage sites.
(a) Dehradun is the capital of Uttarakhand and the second largest district in the state. It has an area of 2,405 square kilometers.
(b) Udhamsingh Nagar is a district in the Kumaon region of Uttarakhand. It has an area of 3,050 square kilometers.
(d) Haridwar is a city in the Haridwar district of Uttarakhand. It is one of the most important Hindu pilgrimage sites. It has an area of 1,200 square kilometers.