B.Sc

Please refer to the link provided below for a list of entrance exams for a course in B.Sc:
https://www.shiksha.com/science/articles/top-bsc-msc-entrance-exams-in-india-blogId-13484
Different colleges have different criterias. Candidate should download the brochure of each college seperately to get a fair idea of their eligibility.

If you want to make your career in the teaching field then B.Ed is a good option.

These are two completely different fields. One leads to management while the other places you in the technical field.
So, first, you have to decide between the two. B.Sc is a good option if you are planning to pursue a career in the scientific field or planning to do a Masters in science.
BBA is mostly opted by commerce students who have an inclination towards the management field. Scope for students opting for a BBA is high who can then go for an MBA and get employed as managers in the administration of firms.
Both have the option to join defence services through the CDS exam or civil services.

No, it is not. After completing B.Sc, you are free to opt for a career of your choice or opt for higher studies, whichever you deem fit.

Yes, you can definitely appear for NIFT entrance exam after completing B.Sc (Hons) in physics.

Different colleges have different admission criteria. Normally, candidates should have the following qualifications to be eligible for B.Sc.
1) Students with 50% at 10+2 level from a recognized education board with science stream can opt for B.Sc.
2) Some institutes also conduct entrance exams for admission into B.Sc.

If you have backlogs in your current course, lateral entry into another university will become difficult. Please check with the admissions department of your institute.

You should pursue a course where your interests lie. Please refer to the link mentioned below for a detailed comparison between the two:
https://ask.shiksha.com/what-is-the-difference-between-b-sc-agricultural-biotechnology-and-b-sc-general-biotechnology-qna-3056566

The career in fashion design is a long term project in one's life and it is one of the best paying industries. Some of the jobs you could explore in fashion design field are as follows:
1) Fashion Designer
2) Fashion Illustrator
3) Fashion Stylist
If your strengths lie in illustration, you should pursue a career as a fashion illustrator.