Dear student,

If you are targeting boards exam, then the current sample papers released by cbse will be very helpful. Also you should practice some previous years question papers, just to get an idea that from which topics the question are framed and then get a rough idea that how the questions can be framed this year as per seeing past years papers.

So, check out the following link to get tye sample papers and previous years questions papers for class 12th cbse :-
https://school.careers360.com/articles/cbse-class-12th-question-papers/amp

And also check out the following cbse official site for previous year paper ( 2020 ) :-
https://cbse.nic.in/curric~1/qpms2020/qp12-2020.html