The Baglihar, Dulhasti, and Salal hydro power projects have been developed on the Chenab River. The Chenab River is one of the major rivers in the Indian state of Jammu and Kashmir. It is a tributary of the Indus River and flows through the states of Himachal Pradesh and Jammu and Kashmir.

Option 1, Chenab and Jhelum, is incorrect. While the Chenab River does flow through Jammu and Kashmir, the Jhelum River is located in the Pakistan-administered territories of Azad Kashmir and Gilgit-Baltistan.

Option 2, Chenab and Indus, is partially correct. The Chenab River is indeed a tributary of the Indus River, but the hydro power projects mentioned in the question are specifically developed on the Chenab River.

Option 3, Ravi, is incorrect. The Ravi River is another major river in the region, but it is not associated with the Baglihar, Dulhasti, and Salal hydro power projects.

Therefore, the correct answer is option 4, Chenab only.