Dear Divya, 

Stream SA is for students who have enrolled in XI standard and secured a minimum aggregate of 75% in Mathematics and Science in X standard. It is 65% for SC/ST/PWD. This is ideal for you if you want to join B.Sc, B.S, B.Stat, B.Math, etc.

Stream SX is for students who enrolled in 10+2 in Science Stream and are aspiring to join Undergraduate Programme in Basic Sciences namely Physics, Chemistry, Mathematics and Biology. 

So you can choose among these 2 based on your interest.