Hello aspirant

For joining ISRO , scientist SC ( entry level) basic qualifications are Msc or B tech. Msc can be in physics or Chemistry or mathematics. After BSc physics you can join as Technical Assistant, ISRO allow you option of part time or correspondence study,after completing msc you can get promoted  to scientist. The following organizations offer jobs in labs and Institutions with over 1000 vacancies every year and recruit the best.

So conclusion is you can do BSC in any of one physics , Chemistry or Mathematics

You can follow the link below

https://engineering.careers360.com/articles/isro-drdo-barc-dae-how-work-here