The correct option is
2 and 3 only
.Explanation
The Gandak is a major left-bank tributary of the Ganga, originating in the high Himalayas of Nepal and flowing south into the plains of India.
- Statement 1 is Incorrect: The Gandak does not comprise a single stream throughout its upper course. It is formed by the union of two streams, namely the Kaligandaki and the Trishulganga. While it is known as the Narayani in Nepal, its formation involves the confluence of these distinct headwaters.
- Statement 2 is Correct: The river rises in the Nepal Himalayas in the region situated between Dhaulagiri and Mount Everest. It drains the central part of Nepal before entering India.
- Statement 3 is Correct: The river enters the Ganga plain in the Champaran district of Bihar. It flows south-east and eventually joins the Ganga at Sonpur near Patna.
Key Takeaway: The Gandak is formed by the confluence of the Kaligandaki and Trishulganga in the Nepal Himalayas and meets the Ganga at Sonpur, Bihar.