Hii Vitista!
All he three fields are of equal importance and are good in thier own ways. The future scope of all the three fields you mentioned above are good. All provide a promising career ahead.
After doing BSc forensic science, you can get employed in fields such as crime investigation, laboratory research, forensic scientist, investigative officers, crime reporter, law consultant etc.,
The salary ranges from INR 3-4 lakhs per annum as a beginner.
After completing BSc life science, you can join fields such as biomedical scientist, research assistant, computational biologist, biochemist, biotechnologist, clinical research associate etc.,
The salary ranges from INR 10,000- 20,000 per month initially.
After BSc Chemistry you can get employment in fields such as agrochemical industries, pharmaceutical industries, chemical manufacturers, forensics, oil and gas related sectors, plastic industries, laboratory research etc.,
The salary ranges from INR 20,000 - 1 lakh per month as per the post.

So, you need to decide the field in which you are more interested and go forward with it.
Hope this helps.
Good luck!