A resolution passed by the Rajya Sabha under Article 249 of the constitution empowering Parliament to legislate on a state subject in national interest remains in force for a period.

The correct answer is C) Not exceeding one year. Under Article 249, Rajya Sabha can pass a resolution by a two-thirds majority of members present and voting, declaring that Parliament should legislate on a State List subject in the national interest. Such a resolution remains in force for one year and can be renewed by a fresh resolution for another year.

Why the others fail:

• A) Six months is the period for which laws made under the resolution continue after the resolution lapses (Article 249(2)). It is not the validity of the resolution itself.
• B) Two years has no basis in the text. Renewal happens one year at a time.
• D) Unlimited is wrong because the resolution must be renewed annually.

The core concept is the temporary federal shift under Article 249, which contrasts with Article 250 (Emergency, where Parliament's power over State List subjects lasts while the Proclamation is in force) and Article 352. For Mains, it is a useful example of the Centre-State balance debate and of the Rajya Sabha's role as the States' chamber.

Trap: aspirants mix up the one-year validity of the resolution with the six-month survival period of the laws made under it.