Many colleges accept class 12 marks as their admission parameter but in IIT and nit it is on the basis of marks scored in JEE mains and advance and in bits pilani only board toppers get direct admission others have to go through bitsat examination process

Top engineering colleges does not give admission just on the basis of 10th and 12th marks they conduct separate entrance test just the colour of the student the top engineering institutes suggest Indian institutes of Technology and National institutes of Technology or other private Institute searches Birla Institute of Technology or Vellore Institute of Technology or SRM all have their entrance test and once you qualify entrance test you can only then get into those colleges.