One of the most prestigious exams at +2 level is KVPY. Now it can be cleared in both 11th(SA) and 12th(SX) and in college as well(SB). I will be talking about SX here, and how to clear it, especially if you are a PCB student.
There is no concrete syllabus for KVPY. But if you follow NCERT syllabus you can clear the exam easily as 99% of questions are asked from the chapters prescribed by CBSE. Now most PCB students are NEET aspirants as well. So to a great extent ones NEET preparation will prove enough to get good marks in KVPY. The books I would suggest are
BIOLOGY: NCERT+ Coaching modules (I used Aakash modules for NEET preparation). Biology is a trump card. In my year (2017) it was really easy whereas it was kinda tough in 2016. I wouldn’t ask you to focus exclusively on any particular topic and instead would suggest reading the whole book properly. But yes, I feel one should read Biotech and Genetics in depth as some weird questions are asked sometimes.
CHEMISTRY: In my opinion the easiest subject in KVPY. Physical is mostly from NCERT, you can practice coaching modules and OP Tandon. As far as organic is concerned, NCERT + Coaching modules + MS Chouhan (Elementary Problems) is more than enough. It’s not necessary to do MS Chouhan but if you solve it, you can even score 100% in organic portion. For Inorganic, NCERT and coaching modules are enough. Very little practical chemistry is asked.
PHYSICS: I wouldn’t recommend you to attempt the second section of physics (2 marks/question section) as Biology and chemistry are far more scoring. As far as section 1 is concerned, NCERT + Coaching modules + DC PANDEY (Medical Edition) are good enough to score around 12–14+/20, if one doesn’t make silly errors. HC Verma, although time consuming can help you get even more, but I would recommend you to focus more on biology and chemistry for KVPY as they are far more scoring.
Otherwise I would recommend just analyzing the past year papers and solving them to get an idea of the level of questions asked. You can opt for an online test series also.
I would finally recommend going with a free mind and giving the paper as KVPY aims to mainly test your basics.