NISER is a National Institute of Science Education and Reserach. It offers Integrated courses. NEST is the entrance examination for admission to NISER. To be eligible for NEST, you should have completed your 10+2 from any recognised board with a minimum aggregate of 60%. It is 60% in General Category and 55% for Reserved Categories. And you should have studied your 12th in regular science stream with a combination of any 3 subjects among Physics, Chemistry, Biology and Mathematics. So even if you do not have Mathematics in your 12th, even if you have Physics, Chemistry and Biology, you are good to go.