An aggregate of 75 % in 12th grade is must for eligibility into NITs in General category or student can be in top 20 percentile of theor board as well for eligibility.

For admission, je emakn scpres will decide your seat allotment  And base don cutoffs you will be granted seats. 

Jemeain cutoff shared below. 

https://engineering.careers360.com/articles/jee-main-cutoff