B.Sc

Hello dear, first clear your aim, because both the courses are different and streams are also different. Believe in yourself, and do according to your interest. Keep calm, relax and think about in which field you see yourself in future. Everything has its own scope, but it is necessary that you have interest in that field. Best of luck.

You have to secure more than 86% in your board exams to join basic science.

No, but you can join OUAT only through your ICAR exam mark.

Yes, you can get B.Sc in Microbiology. You can get admission in Oxford College, but for that you have to qualify their entrance exam. You can get admission there.

If you are SC/ST/NT/OBC, you are luckier, you can get admission with 52% marks.
The case for Bachelors in Arts is opposite. It never went down below 75%, at least not in 2012.
This maybe primarily because, prospective engineers apply for a B.Sc course, in case they don't get a good college.

For seeking admission to the Bachelor of Science course in physics, candidates must have completed their higher secondary examination in science stream and they must have secured good percentage of marks in the physics examination at their 10+2 level.

There are approximately 120 seats.

Hello Subhas,
It's very nice to see your dream of doing M.Sc. Many of us cannot pursue regular courses and then the only option is distance education. I feel IGNOU is the best open university offering hundreds of courses via distance education. Just download brochure cum application form from the NET and follow steps given there.
Best wishes.