B.Sc

I am suggesting you to wait for the cut-off list, 2019, and then you'll get to know the exact chances of your admission. Though you have a good percentage in OBC category, may be you'll get a good college (but not the North Campus).

Yes, Dyal Singh College has B.Sc. Hons in Botany course. As Dyal Singh college comes under University of Delhi, so take admission in this college. You have to first fill the registration form for Delhi university (DU) and then wait for the release of cut offs and then you can apply for the admission in Dyal Singh college on basis of your 12th score only if you met their cut-off requirement. For more details about Dyal Singh College, refer to the following link:
https://www.shiksha.com/college/dsc-dyal-singh-college-lodi-colony-Delhi-2319.

I suggest you to go with B.Tech CSE which has good scope and better opportunities.

Check the below mentioned link for -
Details: www.paruluniversity.ac.in
Apply online: www.puadmission.in

No, it is not necessary while pursuing B.Sc (hons-maths) to have Physics.
You can pursue B.Sc (hons-maths) even without studying Physics.

The fees is 117k for 3 years.

Check out 116 Distance/Correspondence B.Sc in science colleges in India:-
https://www.shiksha.com/science/colleges/distance-correspondence-b-sc-colleges-india

Hi Smiti,
Since you are asking me to compare two completely different subjects, it seems to me, you are interested partly in both. If that's the case, then I recommend going for BCA then MCA. There is a lack of good software for geographical and tectonic surveys and predictions. You might want to make that kind of software yourself when you know how to code. So, if you go for BCA and if you really like geography too, which is a rare case; then later on you can do web research on it and make awesome scientific software that sell, or websites for the same.