The correct answer is option 3, Karakoram. The Karakoram range acts as a watershed between India and Turkistan. A watershed is a boundary or ridge of high land that separates the drainage areas or basins of different rivers. In this case, the Karakoram range separates the watersheds of the rivers flowing in India from those flowing in Turkistan.

Option 1, Zaskar, is not the correct answer as it is a sub-range of the larger Himalayan range, located in the Indian state of Jammu and Kashmir.

Option 2, Kailash, is not the correct answer as it refers to Mount Kailash, a peak in the Kailash Range of the Himalayas. It is located in a remote part of Tibet and is considered sacred by several religions.

Option 4, Ladakh, is not the correct answer as it is a region in the Indian state of Jammu and Kashmir and not a specific mountain range or watershed.

Therefore, the correct answer is option 3, Karakoram.