Hi

Admission in which engineering college are you asking about?.

Anyway,

Biology is not mandatory for getting admission in Btech/engineering

If you have both biology & chemistry then only PCM marks are considered to check eligibility criteria and not PCMB

For example,

To be eligible for BTech in Madan Mohan Malaviya University of Technology, Gorakhpur which is a government institution , one needs to pass 12th with Physics and Mathematics as compulsory/mandatory subjects along with one of - Chemistry or Biotechnology or Biology with at least aggregate of 45% marks (40% if you are from reserved categories ) in  aggregate of these subjects .
You can check the same by visiting our page for which link is given below :-
https://www.careers360.com/university/madan-mohan-malaviya-university-of-technology-gorakhpur/btech-computer-science-and-engineering-course

So,

There's option between biology & chemistry.
Means,

• if you choose chemistry, then only PCM marks will be considered.
  
• If you choose biology then PBM marks will be considered.

So, PCMB marks is not considered in any of the case. It's with either PCM or PBM .

Thankyou