Explanation

In a federal constitutional arrangement, governmental power is partitioned between the Union and regional states, necessitating an institutional umpire:

– Option A is correct: An independent and impartial judiciary is an indispensable structural prerequisite of federalism. It functions as the interpreter and guardian of the Constitution, resolving intergovernmental disputes between the Centre and states (under Article 131) and preventing either tier from encroaching upon the legislative domains delineated in the Seventh Schedule.
– Option B: While the Council of States (Rajya Sabha) represents states, bicameralism alone does not sustain federalism without judicial enforcement of constitutional bounds.
– Options C and D: Regional representation in the Cabinet is a political convention, and judicial enforceability of Fundamental Rights reflects constitutionalism and civil liberties rather than federal state relations.

Therefore, the decisive federal feature is that the independence of judiciary is safeguarded — Option A.