Hey Richa.

Law entrance examinations like CLAT and LSAT can't be taken while you are in 11th Class. They can be taken in the same year you appear in the 12th  Class. These exams are scheduled every year in the month the May-June. The eligibility criteria for CLAT requires you to score a minimum aggregate of 45% marks in 12th boards to be eligible for admission through CLAT. And You need to pass class 12th to be eligible to take admission through LSAT. So you can take these entrances in the same year you appear for 12th boards and your admission will be provisionally based on you scoring the minimum required marks in 12th. Admissions will be done on the basis of your score and rank in the entrance only.

Best of luck