In India, separation of judiciary from executive is enjoined by

Option B is correct. Article 50, a Directive Principle of State Policy, directs the State to take steps to separate the judiciary from the executive in the public services. Directive Principles are non-justiciable, so no court can enforce Article 50 directly, but they guide law-making and policy.

Why the others fail:

• A (Preamble): The Preamble states the ideals of justice, liberty, equality and fraternity. It sets the philosophy but contains no specific directive on separating the judiciary from the executive.
• C (Seventh Schedule): It divides legislative subjects among the Union, State and Concurrent Lists. Entries on courts and administration of justice allocate competence but do not mandate separation.
• D (Conventional practice): Here the separation is a constitutional instruction, not a convention. The Constitution itself names it under Article 50.

Core concept: separation of powers and judicial independence, which the Supreme Court has read as part of the basic structure even though the phrase is absent from the text. Mains angle: the gap between non-justiciable DPSPs and enforceable Fundamental Rights, a recurring GS-II theme. Separation of the magistracy from the executive was carried out state by state over decades.

Trap: Aspirants pick A because the Preamble speaks of justice and separation sounds like a basic value. The explicit mandate sits in Article 50.