Hello Tushar,
Actually, you have to score 75% or in top 20 percentile in the 12th board examination after that only you can get an NIT college or give the JEE Advanced examination to get IITs.
For more information, you may visit the links given below
https://engineering.careers360.com/articles/jee-main-eligibility-criteria
https://engineering.careers360.com/articles/jee-advanced-eligibility-criteria
Thanks for query on this platform, you may visit again for further queries.
All the best.
Regular exam updates, QnA, Predictors, College Applications & E-books now on your Mobile