Which one of the following in Indian polity is an essential feature that indicates that it is federal in character? ​

The correct answer is A. A federation rests on a supreme written Constitution, a division of powers between the Centre and the states, and an independent judiciary that acts as umpire when the two levels disagree. Independence of the judiciary is what lets the Supreme Court decide Centre-state disputes under Article 131 and guard the division of powers. The Supreme Court has also treated federalism as part of the basic structure (S.R. Bommai, 1994).

• B is wrong. Rajya Sabha members are indirectly elected by state legislatures, but that is a design choice, not what makes a system federal. The Lok Sabha is elected by citizens as a whole.
• C is wrong. Ministers are chosen under the parliamentary system (Article 75). Under Article 75(5) a minister who is not an MP for six months ceases to be minister, and the Cabinet has no mandatory link to regional parties.
• D is wrong. Enforceability of Fundamental Rights (Articles 32 and 226) is a feature of constitutional rights protection and exists in unitary states too.

Mains angle: the independent judiciary is the institutional guarantee of federal balance, which is central to questions on Centre-state relations and the role of Governors and President's Rule.

Trap: Candidates pick B because Rajya Sabha represents states. Representation of states at the Centre is a feature of some federations, but it is not the essential criterion the question asks about.