hey,

i hope you are well

the percentage criteria of 12th standard has been removed due to this corona outbreak for getting admission in NITs and IITs , but percentage criteria will be there for the students appearing for JEE mains and advanced in the year 2021 , if you are having percentage less than 75 then you wont be eligible  , to fulfill the percentage criteria i would suggest you to improve your marks by giving improvement exams.

hope this helps!

Yes, you can give the exams, but you may not qualify the eligibility criteria for it.