Hello Kritika sharma

I hope you are doing good . As per your query , I would like to inform you that for becoming a  scientist you have to give Kishore Vaigyanik Protsahan Yojana Exam (KVPY Exam) after your 12th class and score a good rank to initiate your carrer of isro scientist . Eligibilty of kvpy exam is to have atleast 60percent in mathematics,chemistry,physics in aggregate to appear for the exam .Hence you opt science stream with physics,chemistry,mathematics and computer science as your main subject

Hope you found this answer helpful. Good luck for your future