Explanation:

- M.K. Gandhi: He participated in the Second Round Table Conference in London in 1931 as the sole representative of the Indian National Congress.

- Sarojini Naidu: She actively participated in the conference, supporting Gandhi and articulating India’s concerns.

- Pt. Madan Mohan Malviya: He was present at the Second Round Table Conference, representing Indian perspectives.

- Dr. Rajendra Prasad: He did not take part in the Second Round Table Conference. He was active in Indian politics but was not a participant in this particular event.

The correct answer is: Option 4 - Dr. Rajendra Prasad