Physics

No, you can't take admission in B.Tech without having physics in your 10+2.
There are no branches of engineering without physics. You study the basic sciences like Physics and Chemistry and you are introduced to all streams of Engineering. You can expect to study Mathematics for a couple of Semesters at the minimum.

https://www.shiksha.com/b-tech/bitsat-exam
here are the complete details about the BITSAT exam, you can check all the eligibility criteria for different courses.

For example, if the total marks of all 6 subjects you have secured is 300 and the total marks for which the examination conducted is 600, then your percentage will be 50% i.e. , (300/600)*100=50%, so, you need to calculate in the same way to get your percentage for 6 subjects of 12th standard.

Not at all, a guide can just help uh get average marks. But, you need to prepare well refer question papers of last year and prepare thoroughly to get 90%.

At present, M.Sc. Degree holders in Physics, Chemistry, Mathematics and Information Technology are high in demand. After completion of your degree in M.Sc. You can also go for the further higher studies such as research programmes or Ph.D. courses.

The College offers 10 PG courses spread over four faculty members, in the subjects of Economics, History, Political Science, Public Administration, English, Hindi Telugu, Urdu, Mathematics and Commerce. The College also offers Under Graduate courses: B.A. B.Sc. In English Medium and B.Com in both English and Telugu Media.

https://www.shiksha.com/science/colleges/distance-correspondence-m-sc-colleges-india
Here is the list of the college that provides M.Sc. In physics in correspondence mode.

https://www.shiksha.com/university/msu-the-maharaja-sayajirao-university-of-baroda-vadodara-37071
Here are complete details of the college along with all the previous cut-off.