Biology

Yes, you can but only if you are capable of handling that amount of pressure. Both maths and biology are equally tough with vast syllabuses. They will open a lot of opportunities for you in future.

Yes of course, since being a science student, one must have enough knowledge of chemistry, that can help to study B.Sc chemistry.
PS: If one doesn't know anything about chemistry, then it will be very difficult to pursue it.

You can either go for B.Sc zoology or B.Sc botany because in both these courses, there is a combination of both chemistry as well as zoology.

Bachelor of Unani Medicine and Surgery (BUMS):
B.A.M.S
B.M.R.Sc
B.P.Th
B.Sc (Nursing)
B.sc optometry
B.sc. (Hons) medical Technology
B.sc (Hons) opthalmic Technology
Bachelor of Dental Surgery
Bachelor of Pharmacy
Bachelor of Physician Theraphy
Diploma in Clinical Research
M.B.B.S
NDA
Bankings
IAS
IPS
IES
Civil Aviation

Biotechnology and microbiology is having maximum scope in the field of biology.

Yes, you can but before that you will have to crack JEE Mains and then JEE Advance.

Dear,
Geology can be studied after XII (PCM). Admission to university courses is merit or test based and that depends on the university that is offering geology programme.
You can check this link for the different colleges in India and apply accordingly.
https://www.shiksha.com/science/colleges/b-sc-geology-colleges-india
All the best!

Hi,
As per your query, you can consider these options for graduation degree in relations to UPSC:
1. Physics/ chemistry honors.
2. Zoology honors.
3. Psychology.
4. Law.
All the best.