Hi!

Sorry, you cannot pursue bachelor's in science as a correspondence course. The B.Sc. undergraduate degree involves study of theoritical concepts as well as carrying out of different practicals.
The practical examinations carry a significant portion of marks in the overall assessment. That is why, B.Sc. is not available to pursue as an open course.

Some universities abroad do offer B.Sc. in open. You can look for those.

Best wishes!