Relations Between Union and States
Parliament has power to make any law for all or part of India to implement a treaty, agreement, or convention with another country, or a decision of an international conference, association, or body - regardless of whether the subject would otherwise fall in the State List.
This gives Parliament a broad power to legislate on ANY subject - even a normally State List matter - purely to give domestic legal effect to India's international treaty commitments, ensuring India can reliably honour its international obligations without being blocked by the usual internal Union-State division of powers.
This is the constitutional basis Parliament has used to pass domestic laws implementing India's obligations under various international environmental, intellectual property, and human rights treaties and conventions, even where the specific subject matter might otherwise fall under the State List.