CBSE

You can take admission there, but I am not sure about eligible percentage criteria.

Dear Madhur,
Thank you for showing interest in Ganga Technical Campus. Our college is approved by AICTE, recognized by UGC and affiliated to Maharshi Dayanand University. The eligibility to get admission in B.Tech CSE is pass in 12th with Physics and Mathematics as mandatory subject along with one subject out of Chemistry / Biology / Computer Science / Bio Technology with at least 45% marks in the above subject taken together.

Probably not. CBSE allowed only 1 or 2 years of gap between classes.

NIT would be difficult, but you get a government college.

Hi Archan,
Yes, you may get admission for B.Arch in Sir J.J College of Architecture as per your NATA Score.
All the Best!

You will get a CBSE improvement exam marksheet by post at your address which you have given in the application.

It will come after 2 or 3 months of the declaration of result.

Try some agriculture or food technology colleges. Fields are also good to make future and according to your marks. This is suitable for you.

With 80%, it's not easy to get a good college, for more details, check out the link below:
https://www.shiksha.com/humanities-social-sciences/articles/Delhi-university-cut-offs-2018-blogId-17355