Is biology is compulsory to become an astronaut or physics, chemistry,maths is enough to become an astronaut
No, In order to become an astronaut you should choose Physics, Chemistry, and Mathematics as core subjects in 12th. You need to have great mathematics skills. You also need to maintain a good academic record. After 12th you can choose a course in Physics, Chemistry, Maths, or Aerospace Engineering. Do a postgraduation.
After you are done with graduation, you can sit for the exam, which is held by NASA for the recruitment of scientists and astronauts. Or in order to join ISRO, one needs to clear the Joint Entrance Exam which is held by the IITs.
I hope it helps.