B.Sc Physics

Probably No. With only a B.Sc Physics degree, you can't achieve such a prestigious career where Lakhs of aspirants are already in the queue.
To go with an astronaut career, you must have a pilot's license along with a 2-3 year (not sure) professional experience of jet aircraft pilot, and an engineering experience too. Moreover, you will pass through physical tests. Your vision capabilities will also be checked. And, I think there is a limit of heights too.

Eligibility for M.Sc. in Forensic Sciences
Minimum eligibility criteria for M.Sc. in Forensic Science course may vary across institutes. Primarily, the criteria include:
Bachelors degree in science/ engineering / pharmacy/ medicine, obtained from a recognized university.
A minimum aggregate score of 60% at the level of graduation.

If you too are planning to apply for a B.Sc or M.Sc course but are puzzled about choosing the right college, you are certainly at the right place. Given below is the list of top 10 B.Sc/ M.Sc colleges in India in 2016 basis ranking released by India Today.
https://www.shiksha.com/science/articles/top-10-bsc-msc-colleges-in-india-blogId-13473

Please refer to the link provided below for a list of top colleges which offer courses in M.Sc. from India. These are top ranked colleges as reviewed by India Today in the year 2016.
https://www.shiksha.com/science/articles/top-10-bsc-msc-colleges-in-india-blogId-13473

Yes, you are eligible to apply for that.

Yes, physics has good opportunities like in the fields of nuclear Physics, Nuclear Medicine & more.
All the best.

M.Sc. (Information Technology): Eligibility
Candidates can be eligible for admission if they fulfill any of the following conditions:
Bachelors degree in Information Technology / Computer Science / Physics / Stats / Electronics or equivalent examination with at least 45% marks in aggregate from a recognized university.
B.Tech./BE degree holders in Computer Science/Informational Technology are also eligible for M.Sc. IT course.
Aggregate percentage required in graduation or equivalent may vary from college to college.

You may or you may not. Every college has its different guidelines, so contact to your desired college.

Yes, you can complete your B.Sc, but you have to submit gap certificate with a valid reason.