The correct option is (c) 1 and 3 only.
Explanation
The Ganga-Brahmaputra basin is a vast geographical region in the Indian subcontinent, defined by the interaction of two major river systems and situated within the sub-tropical climatic zone.Statement 1 is Correct: The basin is situated in the sub-tropical region, extending approximately between 10°N and 30°N latitudes. This latitudinal extent places it in a zone characterized by a monsoon climate with hot summers and distinct rainy seasons.
Statement 2 is Incorrect: The basin is not drained exclusively by the Ganga. It is formed by the combined drainage systems of the Ganga and the Brahmaputra rivers along with their respective tributaries (such as the Ghaghra, the Son, the Chambal, the Gandak, the Kosi, and the tributaries of Brahmaputra).
Statement 3 is Correct: The Sundarbans delta is a defining physiographic feature of this basin. It is the largest delta in the world, formed where the Ganga and Brahmaputra rivers flow into the Bay of Bengal. The area is renowned for its mangrove forests.
Key Takeaway: The Ganga-Brahmaputra basin is a sub-tropical region (10°N–30°N) formed by the confluence of the Ganga and Brahmaputra river systems, terminating in the Sundarbans delta.