Answer : 3. "B.R. Ambedkar "
Explanation :

B.R. Ambedkar attended all three Round Table Conferences. The Round Table Conferences were a series of discussions held in the 1930s to consider and discuss constitutional reforms in India. B.R. Ambedkar, a key figure in the drafting of the Indian Constitution and a champion of the rights of the Dalit community, actively participated in these conferences.