Hello Aspirant! 

You can sit for the JEE MAINS but you may not get admission into institutions like NIT and IIT because it requires the candidates of UR category to have a minimum of 75% marks in class 12 boards.

Hi

There is no specific passing percentage to sit for JEE Mains, this is because this differs from state to state. 

Now to take admissions for B.Tech oe B.E. you have to get minimum aggregate of 75% of total marks or has to be in the top 20 percentile of the respective Board. 

For further information check this link: https://engineering.careers360.com/articles/jee-main-eligibility-criteria

Best of Luck.

Hope this helps.

Cheers!