Name the President of India who was elected unopposed in the Presidential election, with no other candidate successfully filing a nomination.

Introduction / Context:
The President of India is elected by an electoral college consisting of elected members of Parliament and state legislatures. Normally, more than one candidate is in the race. However, there has been a rare occasion when only one valid candidate remained in the fray, leading to an unopposed election. This question asks you to identify which President was elected in this unique manner.

Given Data / Assumptions:
- The focus is on an unopposed Presidential election, where no rival candidate remained after scrutiny of nominations or withdrawals.
- Four former Presidents of India are listed as options.
- Only one of them was elected unopposed.

Concept / Approach:
Dr. Neelam Sanjiva Reddy is historically noted for being elected as President of India unopposed. In that Presidential election, other candidates withdrew or their nominations were rejected, leaving him as the sole valid candidate. As a result, he was declared elected without a formal contest, making his election unique in Indian Presidential history.

Step-by-Step Solution:
Step 1: Recall that Dr. Neelam Sanjiva Reddy served as President of India and that his election is often highlighted as unopposed. Step 2: Dr. Zakir Husain, Dr. Shankar Dayal Sharma and Dr. Fakhruddin Ali Ahmed all faced normal contested elections. Step 3: The special fact about Dr. Neelam Sanjiva Reddy is frequently mentioned in polity and general knowledge books. Step 4: Therefore, among the listed names, he is the only one fitting the description of being elected unopposed.

Verification / Alternative check:
You can verify in standard reference books on Indian polity or from official election commission information, which records that Neelam Sanjiva Reddy was declared elected unopposed as President after the withdrawal and rejection of other nominations.

Why Other Options Are Wrong:
- Dr. Zakir Husain: Elected through a normal competitive Presidential election.
- Dr. Shankar Dayal Sharma: Also elected after a contest involving other candidates.
- Dr. Fakhruddin Ali Ahmed: Similarly became President through a contested election process.

Common Pitfalls:
A common pitfall is to assume that any widely known President might have been elected unopposed without recalling specific details. Another error is to confuse this unique feature with other famous Presidential elections. To avoid confusion, remember that Neelam Sanjiva Reddy is linked with the special case of an unopposed Presidential election.

Final Answer:
The only President of India elected unopposed was Dr. Neelam Sanjiva Reddy.