Hello Swadhin,

Let me clear up the doubts of eligibility Norma for JEE mains:

• Candidates need to have secured a minimum 75% marks in class XII or equivalent exam or be in the top 20 percentile in their class XII exam conducted by the respective board.
• For SC/ ST candidates, the eligibility criteria are to secure 65% marks in class XII or equivalent exam

Now, if you are a general candidate and you are not in top 20 percentile of your class in your boards exam then you are not eligible for JEE mains. 

And in case you are a SC/ST candidate then you need above 65% marks in 10+2(equivalent qualifying exam) to be eligible. 

I hope your doubts are cleared. 

All the best.