The most biodiversity-rich area in India is:

1. A

   Gangetic Plain

   (a) Gangetic Plain. Densely farmed and settled; diversity is lower than the Western Ghats hotspot.

2. B

   Trans-Himalayas

   (b) Trans-Himalayas. Cold desert (Ladakh, Lahaul rain-shadow) with specialised but not the richest Indian biodiversity.

3. C

   Western Ghats

   (c) Western Ghats. A global biodiversity hotspot: endemic amphibians, plants and fish, high rainfall and habitat mosaic. (c) Official key.

4. D

   Central India

   (d) Central India. Important teak–sal forests and fauna, not the richest block on this list.

Summary. Official key is (c). Among the four, the Western Ghats are India’s most biodiversity-rich area (hotspot with the Sri Lanka unit). The Gangetic Plain, Trans-Himalaya and Central India are poorer or specialised.