M.C. Setalvad, B.N. Rao, and Alladi Krishnaswamy Iyer were eminent personalities who were significant contributors to the Indian legal and constitutional study. This indicates that they did not have a direct affiliation with political parties or labor unions, making option 1 (Swaraj Party), option 2 (All-India National Liberal Federation), and option 3 (Madras Labour Union) less appropriate.
Option 4, Servants of India Society, is an organization founded by Gopal Krishna Gokhale in 1905 to further the cause of Indian`s self-reliant development and welfare. As a society, it had a strong focus on education and legal reforms, which is in line with the professional interests and contributions of these three individuals.
Therefore, option 4, Servants of India Society, is the appropriate answer. Note, however, that all three individuals also played significant roles in the Constituent Assembly of India, so if there were an option reflecting this, it would also be a correct answer.