Step 1: Understand the division of legislative powers.
The Indian Constitution divides law-making powers between the central Parliament and State Legislatures using three lists in the Seventh Schedule (Union, State, Concurrent). Normally, Parliament cannot make laws on subjects in the State List.
Step 2: Know the exceptions.
The Constitution provides for some exceptions where Parliament can legislate on State List subjects. The question asks for the exception based on "national interest".
Step 3: Identify the specific Article.
Article 249 provides the specific mechanism for this. It states that if the Rajya Sabha (the Council of States, which represents the interests of the states) declares by a resolution supported by not less than two-thirds of the members present and voting that it is necessary or expedient in the national interest that Parliament should make laws with respect to any matter in the State List, then Parliament is empowered to do so.
Article 250 relates to a National Emergency.
Article 252 relates to when two or more states consent.
Article 253 relates to implementing international agreements.