You have to give jee mains to get into an admission in NIT's and have to clear JEE advance to get an admission in IIT's . But to give bot the competitive exams there is criteria of mininum 75% in your 12th standard for genenral category students and 60% for other caste candidates.

Hello aspirant

To get seat in any NIT (National institute of technology) and IIT (Indian institute of technology) student must qualify 10+2 with 75% of marks aggregate in physics, chemistry and mathematics. If you score more than 75% , you are eleeleeligi to apply for JEE mains examination.

For more information refer 

https://engineering.careers360.com/exams/jee-main

All the best .

I think by plus two marks you meant class 12th percentage? The you just need to score kinimin of 75 % in board exam in ordef to become eligible to give the exam aprat from that, board percentage plays no role in Jee main counseling. You'll get admission based on your performance in the exam only.

Hope it helps.

Thank you