Hey,
Bachelor of Science(B.Sc) in Chemistry is a three- year undergraduate programme that teaches you about the various aspects of Chemistry.
The general eligibility criteria is to have passed 12th ft a recognised board in Science stream with Chemistry as one of the main subjects.
Most  of the colleges require Mathematics at the 10+2 level for B.Sc in Chemistry course,hence you should take PCM. The University of Delhi takes admission on the basis of 12th marks which includes Mathematics also. While some other colleges conduct entrance exams with questions from Physics,Chemistry,Mathematics and English.
Hope this helps.
Good luck.

Hello faishal it depends on choice of interest you have in these both courses.. but according to what i have searched on your question , i think that PCM would be a better as you have more scope for the jobs so according to me pcm has more scope than PCB also if you like botanical then you can go fot PCB.. 

all the best