Dear Shubh,

If you have completed Class 12 from CBSE or ISCE with required subjects, i.e. PCB and English and have scored requisite percentage in PCB in aggregate, i.e. 50% for general, 45% for PwD and 40% for SC/ST/OBC, then you write the CODE- 2. 

If you have done Intermediate/Pre-degree Examination (PUC) in Science of an Indian University/Board or other recognised examining body with Physics, Chemistry, Biology /Bio-technology including practicals and also English as a compulsory subject, then you write CODE- 3. 

Hope it helps. 

All the best!