The correct answer is option 3, Sikkim. Lake Tsomgo, also known as Changu Lake, is located in the state of Sikkim.

Option 1, Ladakh, is incorrect. Ladakh is a region in the state of Jammu and Kashmir, and Lake Tsomgo is not located there.

Option 2, Himachal Pradesh, is incorrect. Himachal Pradesh is another state in India, but Lake Tsomgo is not located there.

Option 4, Uttarakhand, is incorrect. Uttarakhand is also a state in India, but Lake Tsomgo is not located there either.

Therefore, the correct answer is option 3, Sikkim. Lake Tsomgo is a popular tourist destination in Sikkim and is known for its scenic beauty. It is situated at an altitude of about 12,400 feet and is surrounded by snow-capped mountains. The lake is considered sacred by the local people and is an important pilgrimage site. Visitors can enjoy boating on the lake and also witness the beautiful reflection of the surrounding mountains in its crystal clear waters.