Explanation:

- Dr. Rajendra Prasad (Option 1): He was the first President of India and served two terms. However, he was not elected unopposed; there were other candidates in the elections.

- Dr. Radhakrishnan (Option 2): He was the second President of India. He also did not win unopposed; there was an election.

- Dr. Neelam Sanjiva Reddy (Option 3): He is the only President of India to be elected unopposed, in 1977. No other candidate filed nomination against him.

- Dr. K.R. Narayanan (Option 4): He served as President from 1997 to 2002 and was elected after a contest.

Correct Answer: Option 3 – Dr. Neelam Sanjiva Reddy was elected President of India unopposed.