Core Legal Answer & Context: Repugnancy arises when a law made by the State Legislature conflicts with a law made by Parliament on a subject enumerated in the Concurrent List (List III of the Seventh Schedule). Article 254 of the Indian Constitution governs this situation. Generally, if a State law is repugnant to a Union law on a Concurrent List subject, the Union law prevails, and the State law becomes void to the extent of the repugnancy. However, there is an exception: if the State law, on a Concurrent List subject, has been reserved for the consideration of the President and has received his assent, then that State law shall prevail in that State, notwithstanding its repugnancy to an earlier Union law. Parliament, however, retains the power to enact a subsequent law overriding the assented State law.

Relevant Statutes and Sections: Indian Constitution: Article 254 (Inconsistency between laws made by Parliament and laws made by the Legislatures of States), Seventh Schedule (List III - Concurrent List).

Important Landmark Cases:

1. M. Karunanidhi v. Union of India (1979): The Supreme Court laid down tests for determining repugnancy: (a) direct conflict, (b) Parliament's intention to occupy the whole field, and (c) conflict in the 'pith and substance' of the laws. It clarified that for repugnancy, there must be a direct inconsistency or impossibility of simultaneous obedience.
2. Zaverbhai Amaidas v. State of Bombay (1954): This case affirmed that if a State law on a Concurrent List subject receives Presidential assent, it prevails over an earlier Union law. However, Parliament can subsequently legislate on the same matter, overriding the State law.

Clear Conclusion: In cases of repugnancy between Union and State laws on Concurrent List subjects, the Union law generally prevails. The exception of Presidential assent for State laws provides a limited scope for State law to prevail, but Parliament ultimately retains legislative supremacy through its power to enact subsequent overriding legislation.