Hey aspirant,

If you have separately applied for PCM and PCB you can skip PCB and give PCM. However, if you have applied for PCMB then you will have to face questions for Biology, as the schedule is :-

90 mins for Physics and Chemistry

90 mins for Mathematics

90 mins for Biology

In PCMB you can't skip any part and I would suggest you to attempt everything.

Hope this helps,

All the best!