Hello Avinash!

JEE Advanced is really full of uncertainties. The variation of cutoff marks varies by a wide margin as compared to JEE MAINS. I'll suggest you to keep your score above 240-250 to be on the safer side. It is possible that you may get seat if your score is bit low also but why one should take a chance?

Try pushing your score above 250 and you may get IISER. After JEE ADVANCED the race is mainly for seat in IITs. So the cutoff for IISc and IISER remains bit lower. 

Hope that helps!