Which of the following States/Union Territories of India receives the highest average annual rainfall?

The correct option is Meghalaya.

Detailed Explanation:
Meghalaya receives the highest average annual rainfall among all States and Union Territories in India. In fact, Mawsynram and Cherrapunji, located in the East Khasi Hills district of Meghalaya, receive some of the highest recorded average annual rainfalls in the world, often exceeding 11,800 mm annually.

Reasons for High Rainfall in Meghalaya:
1. Bay of Bengal Monsoon Branch: During the summer, moisture-laden winds from the Bay of Bengal branch of the South-West monsoon travel northwards directly toward the region.
2. Funnel-Shaped Relief Features: The Garo, Khasi, and Jaintia hills create a funneling topology. When the moist monsoon winds enter these valleys, they get trapped and are forced to rise abruptly.
3. Orographic Rainfall: As the air rises along the steep mountain slopes, it cools adiabatically, condenses rapidly, and causes continuous, extremely heavy rainfall (orographic precipitation).

Comparison with Other Listed Regions:
- Delhi: Receives moderate rainfall, averaging around 600 - 800 mm per year.
- Ladakh: A cold desert located in the rain-shadow zone of the Himalayas, receiving less than 100 mm of annual precipitation.
- Rajasthan: Characterized by arid to semi-arid regions (Thar Desert) with an average annual rainfall ranging between 100 mm and 500 mm.