Explanation:

A follower of Gokhale, Narayan Malhar Joshi founded the Social Service League in Bombay with the aim to secure for the masses better and more reasonable conditions of life and work. They organised many schools, libraries, reading rooms, day nurseries and cooperative societies.

Social welfare slowly but inevitably led to labour welfare and labour organisation. 

N. M. Joshi played an important role in the establishment and development of many organisations —the Workingmen's Institute, the International Labour Organisation, the All-India Trade Union Congress, the Indian (now National) Federation of Trade Unions, the Bombay Textile Labour Union, the Mafatlal Gagalbhai Textile Technical School and many other associations for and of labour.

The second Round Table Conference was held in London from September 7, 1931 to December 1, 1931. The Indian National Congress nominated Gandhi as its sole representative. Labour was represented by N. M. Joshi, B. Shiva Rao and V. V. Giri. x Hence option (a) is the correct answer.