Detailed Solution:
The correct answer is “one year”.
Clause (1) of Article 249 of the Indian Constitution states that Parliament can make laws on matters in the State List if the Rajya Sabha passes a resolution with at least two-thirds of its members present and voting.
The resolution can remain in force for up to one year, but can be extended for another year if the Rajya Sabha passes it again.
Any law made by Parliament based on the resolution is only valid for six months after the resolution ends, except for things done before the resolution ended