Which mountain range acts as the major watershed between India and the historical region of Turkistan?

Introduction / Context:
Northern India is bordered by several high mountain ranges that also separate it from Central Asian regions historically referred to as Turkistan. These ranges act as watersheds, dividing river systems that flow south into India from those that flow north or west into Central Asia. This question asks you to identify the specific range that plays this watershed role between India and Turkistan.

Given Data / Assumptions:

• The question refers to a watershed, meaning a divide between river basins.
• The location is between India and the region historically called Turkistan.
• The options are Zaskar, Kailash, Karakoram, and Ladakh ranges.
• We assume basic familiarity with major ranges north of the Himalayas.

Concept / Approach:
The Karakoram range lies to the north west of the main Himalayan range and forms part of India's northern frontier. It extends from the Pamir Knot region and includes some of the world's highest peaks and important passes. This range separates river systems flowing into the Indian subcontinent from those flowing into the Central Asian basins, thereby acting as a major watershed between India and Turkistan. Other ranges like Zaskar and Ladakh are also high, but the Karakoram is most commonly cited in standard exam references as the watershed between India and Turkistan.

Step-by-Step Solution:
Step 1: Identify the region called Turkistan, which broadly refers to parts of Central Asia north of India. Step 2: Recall the major Trans Himalayan ranges north of the main Himalayas: Karakoram, Ladakh, and Zaskar. Step 3: Recognise that the Karakoram range forms India's frontier with countries to the north and north west and separates different river systems. Step 4: Check that standard geography MCQ sources mention Karakoram specifically as the watershed between India and Turkistan. Step 5: Conclude that Karakoram range is the correct answer.

Verification / Alternative check:
Exam oriented geography references and compilations state that the Karakoram range acts as a watershed between India and Turkistan. The range encloses glacier systems such as Siachen and forms the northern barrier of the Indian subcontinent. These descriptions match the idea of a watershed dividing river systems flowing toward India from those flowing toward Central Asia.

Why Other Options Are Wrong:

• Zaskar range: Lies further south within the Trans Himalayan system but is not the primary watershed mentioned in this context.
• Kailash range: Associated with Mount Kailash and the region around Lake Manasarovar, but not identified as the main watershed between India and Turkistan in standard MCQs.
• Ladakh range: Part of the Trans Himalayas, important locally but again not the main watershed against Turkistan in exam keys.

Common Pitfalls:
Students may confuse the different Trans Himalayan ranges because their names appear together in many chapters. Some also mix up Karakoram with Ladakh and Zaskar ranges due to their close proximity. To avoid this, keep in mind a simple association: Karakoram range equals India's far northern frontier and key watershed between India and historical Turkistan in many exam questions.

Final Answer:
The mountain range that acts as a watershed between India and Turkistan is the Karakoram range.