Hi, for IIST admissions the criteria is that you have to get 75% in your class 12 (for SC/ST/PwD its 65%). Moreover, it is important that in JEE Advanced you should score as follows

General Candidates must have scored at least 20% marks(i.e.73 marks out of 366) in aggregate and at least 5% marks (i.e. 6 marks out of 122) in each of the subjects (Physics, Chemistry and Mathematics).OBC NCL candidates have to get atleast 18% marks(i.e. 65 marks out of 366) in aggregate and at least 4.5% marks (i.e. 5 marks out of 122) in Physics, Chemistry and Mathematics each. For SC, ST & PD Candidates- At least 10% marks(i.e.36 marks out of 366) in aggregate and at least 2.5% marks(i.e. 3 marks out of 122) in each of the three subjects (Physics, Chemistry and Mathematics)