Biology Spl

No, you can't do that once you have done your 12th with a particular subject then again you can't give with another subject.

If your Biology fail in HSC Thn you can write the Biology paper only
But if you have taken any other stream other than Science with Biology thn you have to retake from 1 HSC AS Science stream.

As of now students with Biology as an additional subject are eligible for NEET so going by this. Yes, you would be eligible for NEET 2022 if you are a PCM student and giving Biology as an additional /optional subject.

No, that is not possible.
You have to take again HSC with Science for biology.

You can do B.A. In specific subjects but B.Com might be different course as per your Science background it belongs to the commerce background, which includes finance, banking, law, taxation and management.

There is no college in India that offers a combination of this specific course. You might have to pursue either one of them individually. However, if you want to pursue both of these simultaneously, you could apply in some foreign universities that offer this course. Listed below are a few of them:
University of Chester
Lancaster University
Kelle University of Illinois
York University, etc.

Yes, you are eligible for B.Com course from a Science background.
All the best for your career.

If you don't have pcm aur pcb than you can opt to many different courses. B.Com
BBA
Animation and Multimedia. Fashion Designing. Jewelry Designing. Yoga Education. Education Technology. Print Media Journalism. Event Management. Interior Designing.

There is no set cutoff as such but the average board percentage lies somewhere around 92% for both the present batches. However, there are people with board scores as low as in the 70s. Ashoka's selection procedure is holistic and lays equal stress on both academics and curriculars. If you have a slightly low score in the boards but are exceptional in curriculars and the admissions team sees that you have potential, you will be selected.

You have a lot of options as well as opportunities in the near future. You can be an engineer, doctor, professor, startup owner, businessmen, etc. Have a very deep research and start your journey in that field.