Physics

It varies from person to person. If you love doing Maths, then go ahead with it, or else if you love doing physics, then go forth with it, but don't force yourself into one.

Check the last year cut-offs to have an idea of your chances though physics & maths is difficult to get.

You have to qualify in the 12th examination. Otherwise, you can't apply for a Degree Class.

It is B.Sc in computer Science and over this score it is very difficult to get admission in DU. For you I am attaching the official link of the department of computer Science, Delhi University. You can visit this link. http://cs.du.ac.in/programmes/bsc/
This article will help you. https://www.shiksha.com/science/articles/top-colleges-of-du-for-bsc-blogId-16957.

Yes, but it has to be as Delhi University doesn't count marks for PE. If you had taken music, the case would have been different.

Yes, you can just check the cutoff list of DU and have a admission in the college which is preferred by you.
Best of luck.

Hi,
After failing in Maths (and even after 3 years of GAP), it's actually very difficult in get in Astro related degree. However, what you can do is to take admission in any college (may be private) in B.Sc. Physics (If you are in age limit). After B.Sc. Go for M.Sc in Astronomy Specializations.

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You can see the list of top colleges here-
https://www.shiksha.com/design/fashion-design/ranking/top-fashion-design-colleges-in-india/94-2-0-0-0

Yes, you can. Appearing for VITEEE has no constraints. You should have a percentage of 65 percent or 60 to be eligible for getting into it. After appearing for VITEEE, the admission is based on how you score in their entrance examination. You are provided different group according to the marks obtained and fees also varies according to the group's. Group A being the best. Try to score good marks in VITEEE.
All the best.

From my experiences, I can tell you that there is no specific book which can help you or there is no specific book from where they ask questions. Mainly, all the M.Sc Level entrance exam deal with the problems Being a Physics Hons student, I can tell you that to solve this type of problem, you have to clear first your basics. Basically, you need to study various type of book and solve many problems. As you ask which is the best book I will recommend you the book written by S. K TOMAR and you may go through all the study material of FIZIKS.