Explanation:

- The Punjab Reorganisation Act of 1966 divided the old state of Punjab into Punjab and Haryana.

- The main reason was due to linguistic and cultural differences.

- The Shah Commission (Option 3) was set up in 1966 to recommend how the division should take place.

- The Dhar Commission (Option 1) was actually formed in 1948 to look into the reorganization of states on a linguistic basis all over India, not specifically Punjab and Haryana.

- The Dass Commission (Option 2) is not related to the formation of Haryana or Punjab.

- The Mahajan Commission (Option 4) was set up later to address the border disputes between Punjab and Haryana, especially regarding Chandigarh.

Correct Answer:

Option 3 – Shah Commission