Which river meets the Alaknanda at Nandprayag?

Correct answer: Nandakini

The governing concept is the identification of the river pair at a Panch Prayag. At Nandprayag, the Nandakini River meets the Alaknanda, so option A is correct. The similarity between the names Nandprayag and Nandakini provides a useful memory clue, although the answer should rest on the geographical river relationship. Mandakini joins the Alaknanda at Rudraprayag, whereas Tons and Ramganga are separate Himalayan rivers and are not the tributary associated with Nandprayag. Distinguishing similarly named prayags and rivers is important because several questions in this topic use the same Alaknanda system.