Q: Elaborate Article 249 of Indian Constitution ?

Ans: Article 249, the Parliament can make laws on items in the State List if the Rajya Sabha passes a resolution by 2/3rd majority of its members present and voting that it is necessary for the Parliament to make laws on any item enumerated in the State List, in the national interest.

Power of Parliament to legislate with respect to a matter in the State List in the national interest.