The correct answer is (c), Sri. B.N. Rau.
Sri. B.N. Rau was a constitutional lawyer and diplomat who served as the Constitutional Advisor to the Constituent Assembly of India. He was responsible for drafting the Constitution of India, which was adopted on 26 November 1949.
Sri. B.N. Rau was born in 1887 in Mysore, India. He studied law at the University of Madras and the University of Cambridge. After graduating, he worked as a lawyer in Madras and then as a judge in the Madras High Court. In 1923, he was appointed as the Legal Advisor to the Government of India. In this role, he was responsible for drafting a number of important laws, including the Indian Penal Code and the Indian Evidence Act.
In 1946, Sri. B.N. Rau was appointed as the Constitutional Advisor to the Constituent Assembly of India. In this role, he was responsible for drafting the Constitution of India. The Constitution was adopted on 26 November 1949 and came into effect on 26 January 1950.
Sri. B.N. Rau was a highly respected jurist and diplomat. He served as the Indian Ambassador to the United States from 1952 to 1954 and as the Indian Ambassador to the United Nations from 1954 to 1962. He died in 1966.
The other options are incorrect.
(a) Dr. B.R. Ambedkar was a Dalit leader and the principal architect of the Constitution of India. He was not the Constitutional Advisor to the Constituent Assembly.
(b) Pt. Jawahar Lal Nehru was the first Prime Minister of India. He was not the Constitutional Advisor to the Constituent Assembly.
(d) Dr. Rajendra Prasad was the first President of India. He was not the Constitutional Advisor to the Constituent Assembly.