IIT Bombay - Indian Institute of Technology

No, you can't get IIT Bombay by just giving JEE Main.

Yes, prepare yourself for JEE Mains and JEE Advance to get admission in your favorite IIT and also, secure a good rank and percentile to get shortlisted in the merit list.

Both are good options. I will suggest you to once refer their curriculum of these courses from their respective websites. Then judge which course will be better for you. Go through the course. According to me, BS chemistry from IIT Bombay will be a better decision.

*Eligibility Criteria:
1. Minimum 60% required in graduation.
2. Mandatory Course: B.E. / B.Tech (civil engineering)
3. Candidates with AMIE are also eligible to apply.
*Admission criteria of IIT Bombay for M.Tech: IIT Graduates and GATE qualified candidates can apply online with required information on COAP. Candidates selected based on the rank obtained in GATE/IIT merit will be called to appear in a written test in the morning of the first day of the interview. Selected candidates will called for the interview. Candidates are selected based on GATE score/IIT merit and performance in written test and/ or interview.