The exact cut offs are not out yet so nothing sure can be said of the cut offs. That being said, 75% is believed to be the cut off to qualify for JEE-Advance. For OBC, the cut offs will be lower. In order to get a seat in top NITs, 90+ percentile will be a safe bet, 88+ for OBC. At 81 percentile in OBC category, you might have a shot at lower tier NITs in a few courses. 

Good luck.

You will be eligible for jee advance. But with this score you can get only new nits . Your possible colleges are listed below. 

• Nit Patna
• Nit arunachal
• Nit meghalya
• Nit goa

You can also check your possible college as per your score in careers360 college predictor section for jee. Best of luck.