Explanation:

- Climate change vulnerability assessment focuses on understanding how climate impacts people, infrastructure, and ecosystems in specific regions.

- In Himachal Pradesh, the Beas River basin is specifically being studied for climate vulnerability.

- This assessment covers 9,258 villages across four districts, involving more than 1,200 panchayats.

- The other river basins in the state—Ravi, Satluj, and Chenab—have not been the focus of such a broad vulnerability assessment involving such a large number of villages and panchayats.

- Such studies aim to help in climate adaptation planning and disaster risk reduction for communities living along the Beas River.

Option 3: Beas is the correct answer.