Dear Rohith

The Indian Institute of Science Education and Research organises Aptitude Test and to be able to appear you need to clear eligibility criteria.  The cutoff to appear in IISER is 88%. An additional relaxation of 5% is given to OBC candidate.  SC/ST cutoff goes down to 55%. As you have got 90% in PCMB , you are eligible to write IISER Aptitude test. I hope it helped