If you say specifically for 12th CBSE boards then I would say NCERT.
It is literally the best book for one to score above 90% in CBSE board exams. I personally studied NCERT chemistry religiously and managed to score 65/70 in chemistry board exams this year.
So it’s the best if you read the entire NCERT both parts line by line thoroughly and imbibe each and every information given in it along with solving it’s exercises and it will ensure you a really good score. (60+/70)