Which one of the following is not explicitly stated in the Constitution of India but followed as a convention?

The correct answer is C because the Constitution of India does not mandate that every state or region must have representation in the Council of Ministers. There is no specific article requiring a geographical balance in the cabinet. However, it is followed as a long standing political convention to ensure that different parts of the country are represented to maintain federal balance and national integration. Regarding the other options: Option A is incorrect because a Finance Minister can be a member of either the Lok Sabha or the Rajya Sabha. Option B is technically incorrect in this context because Article 75 states that the Council of Ministers is collectively responsible to the Lok Sabha, which implies the Prime Minister must resign if majority is lost. Option D is incorrect because according to the President Discharge of Functions Act 1969, the Chief Justice of India officiates as President in such a scenario, not the Speaker.