Zanskar mountain range separates Himachal Pradesh from

Tibet
Afghanistan
Bangladesh
Pakistan

The correct answer is Tibet.

The Zanskar mountain range is a mountain range in the Himalayas that separates Himachal Pradesh from Tibet. It is a high-altitude range with peaks over 6,000 meters (20,000 feet) and glaciers. The range is a popular destination for trekking and mountaineering.

The other options are incorrect. Afghanistan is located to the west of Himachal Pradesh, Bangladesh is located to the east, and Pakistan is located to the north.