The correct answer is A. Tandi.
The confluence of the Chandra and Bhaga rivers takes place at Tandi, a village in the Chamba district of Himachal Pradesh. The Chenab River is formed at this confluence. The Chenab is one of the five major rivers of the Punjab region. It flows through the states of Himachal Pradesh, Jammu and Kashmir, and Punjab. It is a tributary of the Indus River.
The Chandra River originates in the Pir Panjal Range in Himachal Pradesh. It flows through the Chamba district and joins the Bhaga River at Tandi. The Bhaga River originates in the Dhauladhar Range in Himachal Pradesh. It flows through the Kangra district and joins the Chandra River at Tandi.
The Chenab River is a major source of irrigation and hydroelectric power in the Punjab region. It is also a popular destination for rafting and other water sports.
The other options are incorrect because they are not the places where the Chandra and Bhaga rivers meet. Shimla is the capital of Himachal Pradesh. Arki is a town in the Solan district of Himachal Pradesh. Nalagarh is a town in the Solan district of Himachal Pradesh.