M.Sc

I will like to recommend Nanotechnology over Nuclear physics as it's futuristic technology with applications in diverse fields and good job opportunities in near future.

I can't help you to find a college in Kolkata. but please remove your phone number.
It's not safe to share you phone number publicly.

Refer to the following list of institutes offering your desired course across India. You may visit respective websites in order to find details on fees, intake, eligibility criteria, admission process, entrance exams, learning mode options, etc.
Symbiosis School of Economics
Madras School of Economics
North-Eastern Hill University
Lovely School of Business
Indira Gandhi Institute of Development Research
Pondicherry University
University of Delhi
University of Calcutta
Jamia Millia Islamia
Birla Institute of Technology and Science (BITS-Pilani)
Jawaharlal Nehru University

Ambika, there are many good govt.and private universities around you that are offering M.Sc Botany.
In some of them you need to give entrance test for admission and in some its direct admission or admission based on merit.
Admissions in most of them have started so check their websites for more details.
Good luck.

Hi
Microbiology is a very diversified branch and hence have lot of scope if worked upon diligently.
Read here more and decide.
http://m.timesofindia.com/home/education/news/Micro-world-Career-opportunities-in-microbiology/articleshow/20624271.cms

Hi
If you had mathematics for two years I.e 4 semesters, you are eligible for IIT JAM for M.Sc mathematics.

I have already given answer to your query.
Please go through it.