Correct Option (B)
The correct sequence of Himalayan rivers joining the Ganga downstream of Prayagraj from West to East is Gomati, Ghaghara, Gandak, and Kosi.
- The Gomati River originates in the Gomat Taal (Fulhaar Jheel) in Pilibhit, Uttar Pradesh, and joins the Ganga near Varanasi.
- The Ghaghara River, originating from glaciers near Mapchachungo in Tibet, joins the Ganga at Chhapra, Bihar, to the east of the Gomati's confluence.
- The Gandak River, originating in the Nepal Himalayas, meets the Ganga at Sonpur, near Patna, further east of the Ghaghara's confluence.
- The Kosi River, with its source north of Mount Everest in Tibet, joins the Ganga near Katihar district in eastern Bihar, making it the easternmost among the given rivers.
Incorrect Options:
- Options 1, 3, and 4 present incorrect sequences of these rivers.
- Option 1 incorrectly places Ghaghara before Gomati. The Gomati River joins the Ganga to the west of the Ghaghara's confluence.
- Options 3 and 4 incorrectly place Kosi before Gandak. The Gandak River joins the Ganga to the west of the Kosi River's confluence, meaning Kosi is further east.