The correct answer is (d) None of the above.
The number of ministers have not been limited to 15% the total number of members of the lower house by any constitutional amendment. The number of ministers in the Union Council of Ministers is determined by the Prime Minister, and is subject to the approval of the President. The number of ministers in a state government is determined by the Chief Minister, and is subject to the approval of the Governor.
The Ninety-first Amendment to the Constitution of India, enacted in 2003, inserted a new Article 338A, which provides for the appointment of a National Commission for Scheduled Castes. The Ninety-second Amendment to the Constitution of India, enacted in 2003, inserted a new Article 338B, which provides for the appointment of a National Commission for Scheduled Tribes. The Ninetieth Amendment to the Constitution of India, enacted in 2001, inserted a new Article 338, which provides for the appointment of a National Commission for Minorities.