The correct answer is option 4, Babu Rajendra Prasad. He was the first President of India and he served two terms in office. Option 1, S. Radhakrishnan, was the second President of India but he only served for one term. Option 2, K.R. Narayanan, served as the President of India but he also only served for one term. Option 3, Neelam Sanjeeva Reddy, served as the sixth President of India but he also only served for one term. It is important to note that the question specifically asks for the President of India who held office for two terms, which is why the correct answer is option 4, Babu Rajendra Prasad.