The correct answer is option 3, M. N. Roy. M. N. Roy was an Indian philosopher, political activist, and one of the founding fathers of the Communist Party of India. He was a strong advocate of a philosophy called `radical humanism`.

Option 1, Annie Besant, was a prominent British socialist, women`s rights activist, and theosophist. While she was involved in various social and political causes, she did not specifically advocate for radical humanism.

Option 2, Raja Ram Mohan Ray, is often referred to as the Father of the Indian Renaissance. He was instrumental in the abolition of the practice of Sati and advocated for women`s rights, education, and religious reform. However, he did not specifically advocate for radical humanism.

Option 4, V. D. Savarkar, was a prominent Indian independence activist and the founding member of the Hindu nationalist organization, the All India Hindu Mahasabha. While he had his own ideological beliefs and advocated for Hindu nationalism, he did not specifically advocate for radical humanism.

In conclusion, M. N. Roy, option 3, was the advocate of `radical humanism` among the given options.