CBSE 12th

Hi Keval,
You need to specify your plans and interests for better guidance. Most importantly, mention your stream.

Hi Arnav,
Please clarify if you are enquiring about MIT, USA or Madras Institute of Technology or Manipal Institute of Technology in India.

Hi Mukilan,
You have many options such as MBBS, BAMS, BDS, B.Sc Biology, B.Sc Agriculture, B.VSc, B.Sc Food and Nutrition, B.Sc Health Sciences, etc. What you choose will depend on your likes and dislikes. You can find out about the career options in the fields and figure out your own career aspirations and decide.

Hi,
Please mention your stream for better guidance and suggestions.

Hi Anirudha,
There are many competitive exams one can write such as JEE Mains, JEE Advanced, BITSAT, VITEEE, NATA, NDA, Indian Maritime University Common Entrance Test, Indian Army Technical Entry Scheme, NIFT and so on depending on one's own interests. One can also attempt the state/college common entrance tests.

Please refer to the link provided below for details regarding admissions in B.Sc. course after completion of 12th (HSC).
https://www.shiksha.com/science/articles/what-is-bsc-course-all-about-know-the-full-form-eligibility-scope-blogId-13262

12th will be a good idea but the rest is your choice.

No, only your B.Tech result will matter.

No, it doesn't matter in all institutions as most of them consider the scores of graduation (B.Tech) but it matters in many institutes.