How to take science stream in class 12 in nios?
You need to visit the NIOS website nios.ac.in or the Student portal of NIOS sdmis.nios.ac.in to apply. Here is the link given below for the further instruction & read Page no. 8 & 9 to apply for NIOS.
http://nios.ac.in/media/documents/prospectus/ACADEMIC_PROSPECTUS_2018_19_FINAL.pdf
Good Luck!