hi there,
as you have asked, I want to tell you that there are various colleges in Tamilnadu where you can pursue BSc in botany and physics. 1st of all I am writing some top colleges in Tamilnadu along with the eligibility criteria where you can build your career.

1. Loyola College, Chennai, Tamilnadu
    You should have completed your 10+2 with Biology, Physics and Chemistry or Zoology, Biology, Chemistry, Physics / Biotechnology and for Physics you should have math in you 10+2 in additional. And the admission is on the basis of merit list.
It has a good rating of the placement and has good reviews for both of the academic session and the faculty. And know as one of the best colleges in Tamilnadu.

2. Madras Christian College, Chennai
   You should have completed higher Secondary exam with Physics, Chemistry, and mathematics as compulsory subjects with at least 50% average marks. And the selection procedure is on the basis of merit list along with entrance test. Here the placement matter is quite average whereas the academic and the faculties are good enough for your academic career.
  

3. Stella Maris College, Chennai
  You should have passed 10+2 with "Biology, Chemistry & Microbiology (or) Botany, Zoology, Chemistry / Biotechnology" and mathematics for physics. The selection procedure is based upon the merit list. This college has earned its fame through the academic career and the faculties it has. However, the placement is quite average as compared to Loyola College, Chennai.

4. Ramakrishna Mission Vivekananda College, Chennai
    You should have passed 10+2 in Science stream with relevant subjects and the selection is based upon the merit list. As compared to other colleges, It is a little bit above the average in placement and the academic session. Where as the faculties are enough good.

5. Guru Nanak College, Chennai
    You should have completed your 10+2 with Chemistry, Physics, Mathematics, Bio-Tech Biology/Computer Science. As this is a private college so the selection procedure is based on both entrance and merit list. It has a good academic session along with it the placement record is good enough.

There are many other renowned colleges in Tamilnadu where you can study. But the thing is where you want to study and what you want to do later on. Accordingly, you can choose a better one. Let me know if you want to know about more colleges.

Thank you and best of luck.