0. The Council of Ministers headed by the Prime Minister is responsible to:
The Council of Ministers is collectively responsible to the Parliament, particularly the Lok Sabha, as per Article 75(3) of the Constitution.
Option A: Prime Minister
Incorrect. He is the leader, but not the authority to whom the Council is responsible.
Option B: President
Incorrect. The President appoints them but they are not accountable to him.
Option C: Parliament
Correct. Specifically, they are responsible to the Lok Sabha.
Option D: Speaker of Lok Sabha
Incorrect. The Speaker is a presiding officer, not a body of accountability.