The correct option is Submarine mountains.
Explanation
The Indian territory includes two major island groups: the Andaman and Nicobar Islands in the Bay of Bengal and the Lakshadweep Islands in the Arabian Sea. These groups possess distinct geological origins, with the former being tectonic and volcanic in nature, and the latter being biogenic (coral).
Detailed Analysis:
- Submarine mountains is Correct: The Andaman and Nicobar Islands are believed to be an elevated portion of submarine mountains. Geologically, they are the southward extension of the Arakan Yoma range of Myanmar. This submerged mountain chain is formed due to the collision between the Indian Plate and the Burma Minor Plate.
- Coral reefs is Incorrect: While the Andaman and Nicobar Islands possess fringing coral reefs, the islands themselves are not primarily formed by coral accumulation. In contrast, the Lakshadweep Islands are entirely of coral origin (atolls).
- A sunken continent is Incorrect: The islands are not remnants of a sunken continent but are elevated peaks of a submerged mountain ridge formed by tectonic uplift and volcanic activity.
- A river delta is Incorrect: A river delta is a depositional landform created by sediments at a river's mouth (e.g., the Ganges-Brahmaputra Delta). These islands are structural landforms, not depositional features.
Key Takeaway:
The Andaman and Nicobar Islands are the submerged extensions of the tertiary mountain system (Arakan Yoma), whereas the Lakshadweep Islands are formed by coral deposits.