Exam

You can study from any random book which consists of QA, Verbal Reasoning, Business awareness, and Reading comprehension. I had studied from a book of Arihant publication.

JEE Mains doesn't require class 12th marks. You've qualified the exam. For sure, you'll be getting an NIT but make sure you know about the campus very well because not all NITs come up with good packages.
All the best.

It is somewhat possible for you to get a college. You can use Shiksha's college predictor tool for finding the colleges:
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor?utm_source=cconnect&utm_medium=CR_JEECP&utm_campaign=5836167

Check your chances of getting engineering colleges through this link:
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor?utm_source=cconnect&utm_medium=CR_JEECP&utm_campaign=6375912.

Hi,
Check your chances from this link:
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor?utm_source=cconnect&utm_medium=CR_JEECP&utm_campaign=6375912.

Hi buddy,
Go through this link to check your chances of getting government colleges:
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor?utm_source=cconnect&utm_medium=CR_JEECP&utm_campaign=6375912.

Since COMEDK exam is taken online so it's hard to get the previous year question papers. However, you can get some of the sample questions either online or some of the books published by the known publisher which are easily available in the market.

Yes, you can. The criteria of 75% is only for providing NITs.