Hey Khushi! Students who want to apply for KVPY and are in 12th standard come under Stream SX. 

Students enrolled in XII Standard/ (+2) (Science subjects) during the academic year 2019–20 and aspiring to join undergraduate program in Basic Sciences namely Physics/Chemistry/Mathematics & Biology leading to B.Sc./B.S./B.Stat./B.Math./Int. M.Sc./Int. M.S. for the session 2020–21 provided they have secured a minimum of 75% (65% for SC/ST/PWD) marks in aggregate in MATHEMATICS and SCIENCE subjects (Physics/Chemistry/ Biology) in the X Standard Board Examination during the academic year 2017-18 are eligible to appear for the Aptitude test. While registering for kvpy you must select stream SX. Hope this may help you.