The correct answer is option 2 - Dr. B.R. Ambedkar. He was the chairman of the Drafting Committee, which was responsible for drafting the Constitution of India. The Drafting Committee was formed in August 1947, and Dr. Ambedkar led the committee as its chairman. He played a crucial role in drafting and framing the Indian Constitution, which was adopted on 26th November 1949, and came into effect on 26th January 1950. Dr. Ambedkar was a renowned scholar, jurist, and social reformer, and he made significant contributions to the drafting of the Constitution. His vision and expertise were instrumental in shaping the constitution and ensuring the rights and welfare of all Indian citizens.