Rudraprayag is a town in the state of Uttarakhand, India. It is located at the confluence of two rivers, the Alaknanda and the Mandakini. The Alaknanda river is one of the major tributaries of the Ganges and originates from the Satopanth Glacier, while the Mandakini river originates from the Chorabari Glacier.

Option 1: Bhagirathi is not the correct answer. The Bhagirathi river is also a major tributary of the Ganges, but it does not meet the Alaknanda river at Rudraprayag.

Option 3: Nandakini is not the correct answer. The Nandakini river is another tributary of the Alaknanda river, but it does not meet the Alaknanda at Rudraprayag.

Option 4: Dhauliganga is not the correct answer. The Dhauliganga river is a tributary of the Alaknanda, but it does not meet the Alaknanda at Rudraprayag.

Therefore, option 2, Mandakini, is the correct answer as it accurately identifies one of the rivers that meets at Rudrap