When the offices of both the President of India and the Vice President of India fall vacant simultaneously, which constitutional authority acts as the President of India until a new President is elected?

Introduction / Context:
The Constitution of India provides for continuity of the highest constitutional office, that of the President of India, even in extraordinary circumstances. Normally, the Vice President acts as President when the office of President falls vacant. However, the question addresses a more unusual situation: when both the President and Vice President's offices are vacant at the same time. Understanding who acts as President in such a case is important for examinations dealing with emergency constitutional arrangements.

Given Data / Assumptions:
- The options mention the Prime Minister of India, the Chief Justice of India, the Speaker of Lok Sabha and the Comptroller and Auditor General of India.
- The question specifies that both the offices of the President and the Vice President fall vacant simultaneously.
- It is assumed that the student is aware that, under normal circumstances, the Vice President is the one who acts as President when there is a vacancy in the President's office.
- The situation described is exceptional and handled by specific constitutional practice and precedent.

Concept / Approach:
When the office of the President becomes vacant, the Vice President acts as President until a new President is elected. If both offices are vacant, there is a constitutional need for an interim arrangement to ensure that the functions of the President continue. Constitutional practice and historical precedent indicate that the Chief Justice of India, or in the absence of the Chief Justice, the senior most Judge of the Supreme Court, may be appointed to discharge the functions of the President. This was seen when the Chief Justice acted as President upon the resignation of a Vice President who had been acting as President. The approach is to recall this arrangement and match it with the options.

Step-by-Step Solution:
Step 1: Recognise that the Vice President ordinarily acts as President in the event of a vacancy in the office of President. Step 2: Note that the question specifically states that both the President and Vice President offices fall vacant simultaneously; therefore the normal arrangement is not available. Step 3: Recall the precedent where the Chief Justice of India, or in the Chief Justice's absence the senior most Judge of the Supreme Court, was appointed to discharge the functions of the President when both offices were not simultaneously occupied. Step 4: The Prime Minister, the Speaker of Lok Sabha and the Comptroller and Auditor General do not have any constitutional provision assigning them the role of acting President in this specific situation. Step 5: Therefore, the authority who acts as President in such a situation is the Chief Justice of India, making that the correct answer.

Verification / Alternative check:
Verification can be carried out by studying the historical example of Justice Mohammad Hidayatullah, who acted as President of India when the office of President was vacant and the Vice President had resigned to contest the presidential election. This established the practice that the Chief Justice may be appointed to act as President in such extraordinary circumstances. Standard polity references also explain that, if both the offices fall vacant, the Chief Justice or the senior most Judge of the Supreme Court may be called upon to discharge the functions of the President until a new President is elected, confirming the answer.

Why Other Options Are Wrong:
Option A (Prime Minister of India) is wrong because, although the Prime Minister heads the Government and wields significant executive power, the Constitution does not provide that the Prime Minister shall act as President in these circumstances.
Option C (The Speaker of Lok Sabha) is wrong because the Speaker's role is to preside over the House of the People and maintain order in the Lok Sabha, not to act as President when vacancies occur in the highest executive office.
Option D (The Comptroller and Auditor General of India) is wrong because the Comptroller and Auditor General is a constitutional authority responsible for auditing the accounts of the Union and the States and has no role in acting as President.

Common Pitfalls:
A common pitfall is to assume that the Prime Minister, being the most politically powerful figure, would automatically assume the role of acting President in any crisis, but this is not what constitutional practice indicates. Another mistake is to confuse the rules on presidential succession with those in other countries, such as systems where speakers or parliamentary leaders are placed next in line. In India, the arrangement involves the judiciary through the Chief Justice or a senior Judge, reflecting a different constitutional design. Remembering the historical precedent and the distinction between political and constitutional roles helps avoid these errors.

Final Answer:
When the offices of both the President and the Vice President fall vacant simultaneously, the functions of the President are discharged by the Chief Justice of India (or in the Chief Justice's absence, the senior most Judge of the Supreme Court) until a new President is elected.