IIT

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.

Hello Ramasai,
For architecture courses, you need to clear JEE Mains paper 2 and JEE Advanced. To get admission into IITs for B. Arch courses, you need to clear an Architecture aptitude test (AAT) based on which you will be allotted seats.
However, JEE Mains paper 2 scores are being accepted by many reputed colleges.

Both are very different profiles and have good pay. And mind it, both require a lot of preparation and dedication. Aviation is the second after Bollywood in India in terms of Glamour. IIT engineering also has a very good pay.

Yes, it is possible to get admission in IIT without coaching (when at the time of exam your mind in genius position).

Physics- TMH Publication, IE Irodov and HC Verma.
Maths-IIT Maths by Das Gupta and TMH Publication.
Chemistry-Numerical chemistry by P Bahadur, inorganic by Pradeep Publication or Arihant and organic by Solomon and Fryle or Reso notes.

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

Hello Naimish,
Here are few good colleges apart from IIT which you can join if you failed to get admission into IIT and NIT:
BITS-Pilani
IIIT-Hyderabad
Indian Institute of Space Science and Technology
Anna University
DTU, Delhi
IIIT, Allahabad
NSIT, Delhi
Jadavpur University
BIT-Mesra and Ranchi
PSG College of Technology
Institute of Chemical Technology, Mumbai
PEC University of Technology
IIEST, Shibpur
TIET, Patiala
HBTU, Kanpur
IIIT, Gwalior
College of Engineering, Pune