Hi Rahul 

This is Ritika

If you want to take admission in government Bihar engineering college then the eligibility criteria is that you must have a domicile certificate of Bihar.

Then you can apply for BCECE and based on merit rank you can get college.

If you want to take admission in private college then some take admission on based of your jee main rank and some have another mode of taking based on college and their rule

Hope my answer helped you

Thank you

Hi Rahu
For admission in engineering college the eligibility criteria for all states is almost same . But if you are thinking for getting admission in NIT or IIT Patna then you should have at least 75% marks in science stream in 12th and valid Jee main score but if you want to engineering in Bihar in state government college then eilgibility criteria will be 50%pcm and valid entrance examination of state government college in bihar.
Hope you understand
Good luck