Explanation:

- The Union Constitution Committee of the Constituent Assembly was tasked with framing the political structure and governance model for India.

- B.R. Ambedkar was the Chairman of the Drafting Committee, responsible for drafting the overall constitution.

- J.B. Kripalani was not involved as a chairman of any main constitutional committee, though he was an active member of the Constituent Assembly.

- Jawaharlal Nehru, as an eminent leader, chaired the Union Constitution Committee of the Constituent Assembly.

- Alladi Krishnaswami Ayyar made significant contributions to the drafting process but did not chair the Union Constitution Committee.