NIT

Opening and closing rank of college is based and varies a lot from college to college and also on engineering stream. Please specify the colleges and stream for better assistance.

Let me clear few things. To get admission in IIT, one must clear JEE Mains as well as JEE Advance with good ranking.
For NITs admission, you need not appear for JEE Advance. A good rank in Mains is enough.
Next comes OBC category. Unlike SC/ST or OBC, there are two categories further. Creamy layer and non-creamy layer. If your family income is up to Rs.5 lakhs, you are non-creamy layer. But, if it is above that, you will be treated as creamy layer and you will be treated as general category student.
And, you don't need to score a 90% marks in your class 12th boards. In fact, 70% marks is the eligibility criteria for JEE Mains.

According to ranking, it's Warangal, Suratkal and Allahabad.

There are few good universities that accept JEE Mains scores like Thapar University, Punjab Engineering College, Delhi Technological University and NSIT.

Hello Gautam,
BITS-Pilani, KIIT College, VIT University, PES University, Thapar University, Sastra University, Anna University, DTU Delhi, NSIT-Delhi, PGS College, BIT-Mesra and HBTU-Kanpur are best colleges apart from IIT and NIT.

Firstly, you have to score more than 75% marks in class 12th or be in top 20 percentile of your board for being eligible for admission and then you have to score more than 150 marks to get admission into NIT, Warangal.

Based on the marks of class 12th, you are not eligible for admission in NITs.

Hello Abhishek, Kindly check the attached link, That will help you to make your preferences
http://blog.askiitians.com/top-nits-learning-mechanical-engineering-basis-jee-main-closing-rank/
Good luck.
Thank you.

Check out the JEE Mains 2018 Eligibility Criteria to clear every single doubt coming in your mind.
According to this, the candidates who have scored at least 75% marks in the 12th class are only eligible for appearing in the JEE Mains exam.
So, if you can't appear in the JEE Mains exam, then you can can't get admission in any of the NITs or IITs.
If you haven't scored 75% in 12th, then you can go for the improvement exam or the NIOS exam.
Hope this will help.
All the best.

You should have 70-85 percentile in CAT to get admission in top colleges.