The correct answer is option 2, Dr. Neelam Sanjiva Reddy. He was elected unopposed as the President of India. It means that no other candidate contested against him in the presidential election.

Option 1, Dr. Shankar Dayal Sharma, is incorrect because he was not elected unopposed. He faced competition in the election for the presidency.

Option 3, Dr. Fakhruddin Ali Ahmed, is also incorrect as he was elected as the President of India through a regular election in which there were other candidates as well.

Option 4, Dr. Zakir Husain, is also incorrect as he was elected as the President of India through a regular election and faced competition from other candidates.

In summary, Dr. Neelam Sanjiva Reddy was the President of India who was elected unopposed.