Science

You should opt for B.Sc. in nutritionist. You should prepare for EMCET and get good rank in there.

Combustion means burning of something in the presence of air. Oxidation means gain of oxygen due to any reaction.

You must opt for B.Tech in aerospace engineering or BE in aeronautical engineering.
You can opt for colleges like:
1. IIT's
2. NITs.
3. BITS – Pilani.
4. VIT – Vellore.
5. SRM University.

With your qualifications you can easily get job of developer and tester in any IT company or IT department of an enterprise. You can also get teaching, R&D, government job, a public sector banking job and defence & paramilitary jobs.

It is a good idea, but you have done B.Sc in physics, then you have lot of scope. You can go for M.Sc and explore the world with the knowledge of physics.
Best of luck.

No, it is not necessary. You can show what you have done.

Both subjects have equal importance. If you choose chemistry then you will be able to apply as a teacher and do lab work in laboratories and companies. If you choose microbiology then you will be able to apply for teacher jobs. Both subjects are demanding in Masters degree and PhD degree. Both have many opportunities in research project. So, you can choose according to your interest.

You must fill IIT-JEE Mains application form. If you want to get admission in VIT or any engineering college of West Bengal then you can fill VITEEE application form or WBJEE application form. You can check on https://Shiksha.com for other engineering entrance exam applications.