The correct answer is option 1, B.R. Ambedkar. He was the only person out of the given options who attended all the Three Round Table Conferences. The Round Table Conferences were a series of meetings held in London from 1930 to 1932 to discuss the constitutional reforms for India. B.R. Ambedkar, who later became the principal architect of the Indian Constitution, actively participated in these conferences and advocated for the rights of the oppressed classes. He played a significant role in shaping the future of India by presenting his ideas regarding caste discrimination, minority rights, and social reforms during these conferences. It is important to note that the other options given - M.M. Malavia, Vallabhbhai Patel, and Gandhiji - did not attend all the Three Round Table Conferences.