Hello Ashna!
B.Sc. in Defence Studies is an undergraduate programme of 3 years duration. Candidates of Science stream qualifying their (10+2) level from any recognized board are eligible to apply. Those passing Class 12th from National Open Schools can also apply. In addition to this, you may need to have passed in Mathematics in your Class 12th for some colleges.

The subject combination offered by different colleges and universities may vary. It may include Mathematics and Physics as pass courses in some institutes. But its syllabus as prescribed by the educational institutes providing this course includes the following major topics :
1. Indian's National Security - Introduction to Defence Studies,  Economic aspects of Defence and Security etc.
2. Warfare and Indian Armed Forces - Map reading, Weapon system, functional organizations of Indian Army, Military history etc.
3. India and its neighbouring countries, Defence production and procurement, Recruitment systems, Armed Forces and Society.

Hope this answer will help you.