Hello,

B.Sc ( Bachelor of Science) is a three years Undergraduate Courses. And you don't need to appear for JEE MAINS or JEE ADVANCED to get Admission into a BSc Course. JEE MAINS is conducted to offer Admission in various Undergraduate Engineering courses such as B.Tech (Bachelor of Technology) or B.E (Bachelor of Engineering). The duration of any Course is four years.

Now, JEE MAINS is conducted the offer Admission into various NITs (National Institute of Technology) GFTIs (Government Funded Technical Institutions) and IIITs (Indian institute of Information Technology). Whereas to get a seat in IITs JEE ADVANCED is conducted. Remember only those candidates can appear for JEE ADVANCED who qualify JEE MAINS. To qualify JEE MAINS, Candidates have to Rank among the top 250000 rankers.

If you don't want to go for B.Tech then why want to appear for JEE MAINS and Advanced. You just need to appear for any entrance exam (If University accepts Admission on the basis of entrance exam) or your admission will be done through merit basis, it totally depends on the University you're willing to take admission into.

Good Luck.