22.
The answer is: C
Explanation
The correct option is C: B.N Rao.
B.N. Rao served as the Constitutional Advisor to the Constituent Assembly of India. He played a crucial role in providing legal expertise and guidance to the members of the Constituent Assembly during the drafting of the Indian Constitution. While other leaders like Dr. Rajendra Prasad, Dr. B.R. Ambedkar, and Jawaharlal Nehru were important figures in the Constituent Assembly and played significant roles in the framing of the constitution, none of them held the specific position of Constitutional Advisor.