Concept:
The Constitution generally distributes legislative powers between the Union and the States through the Union List, State List, and Concurrent List. However, Article 253 creates an important exception by empowering Parliament to legislate for implementing international treaties, conventions, and agreements, even on matters that normally belong to the State List.
Step 1: Understanding Article 253.
• Article 253 begins with a non-obstante clause and gives Parliament special legislative power.
• Parliament may enact laws for implementing any treaty, agreement, or convention entered into with foreign countries.
• This power exists irrespective of whether the subject falls in the Union List, Concurrent List, or State List.
Step 2: Application to environmental agreements.
• Environmental protection may involve matters that ordinarily fall within State jurisdiction.
• When India undertakes obligations under an international environmental convention, Parliament can enact legislation to fulfill those obligations.
• Famous examples include environmental statutes enacted following international conferences and commitments.
Step 3: Why other options are incorrect.
• Article 250 applies during a Proclamation of Emergency.
• Article 252 requires a resolution passed by two or more State Legislatures.
• Since no such resolution has been passed, Article 252 is inapplicable.
• Therefore, Article 253 is the correct source of legislative competence.
Article 253 enables Parliament to implement international obligations even on matters otherwise falling within the State List.
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\boxed{\text{Correct Answer = (C) Article 253}}
\]