When the posts of the President and Vice-President of India fall vacant, the Chief Justice of India will act as the President of India. This provision is mentioned in Article 65 of the Constitution of India.

Explanation:
- According to Article 65 of the Indian Constitution, in the event of a vacancy in the office of the President and the Vice-President, the Chief Justice of India (CJI) shall act as the President.
- This provision ensures continuity in the functioning of the government and avoids any power vacuum in the absence of the President and Vice-President.
- The Chief Justice of India is the highest-ranking judicial officer in the country and is responsible for the administration of justice and the interpretation of the Constitution.
- When the CJI acts as the President, he temporarily relinquishes his judicial duties and assumes the executive responsibilities of the President.
- During this period, the CJI exercises all the powers and functions of the President, including the power to appoint judges, pardon convicts, and represent India in international affairs.
- It is important to note that the acting President's term is temporary and lasts only until a new President or Vice-President is elected or appointed.
- The President and Vice-President of India are elected by an electoral college consisting of members of both houses of Parliament as well as members of the State Legislative Assemblies.
- The President is the ceremonial head of state and also wields certain executive powers, while the Vice-President assists the President in the discharge of his duties and acts as the Chairman of the Rajya Sabha (Upper House of Parliament).
- In the absence of both the President and Vice-President, the Chief Justice of India assumes the responsibility of acting as the President to ensure the smooth functioning of the government and the continuity of constitutional processes.