Explanation:

- Option 1: Jyotiba Phule

- Jyotiba Phule was a social reformer and writer, best known for his efforts in women's education and the eradication of caste discrimination in colonial India. He didn't author "Why I am an Atheist."

- Option 2: Raja Ram Mohan Roy

- Raja Ram Mohan Roy was a prominent social and religious reformer who played a key role in abolishing the practice of sati and modernizing Indian society. He is not associated with "Why I am an Atheist."

- Option 3: Bhagat Singh

- Bhagat Singh, the Indian freedom fighter, wrote "Why I am an Atheist." It is an essay where he explains his atheist beliefs and the reasoning behind them.

- Option 4: BR Ambedkar

- BR Ambedkar was a social reformer and the principal architect of the Indian Constitution. While he wrote extensively on social and political issues, he is not the author of "Why I am an Atheist."