is bitsat for free education of btech for 4years??

Hello,
It will be free if you get. Reimbursement from national government or state government or from the institute. Institute mostly give scholarship. You can pay them to the college as miscellaneous amount.
In reimbursement you don't have to pay tuition fees or academic fees but you have to pay for transportation, placement,management, maintainance etc. This amount will be around 30k-35k.So if you get any scholarships then your amount will get even on both side.
In this way your BTech 4 years study will be free.
You anyhow have to pay but in the sense you are getting scholarship you won't have to pay from your account.
Hope it helps!