Hello Kranthi kumar 

It depends on the branch.

Gate Score is important than Rank in case of IISc. Every department releases there Gate Score based cut offs. It’s good to be in 95 percentile if you want to come to IISc, having said that I have not seen any student who was below rank 50 in campus.

So, better try to get a rank in top 100 to get IISc Bangalore.

So, in terms of score i would suggest to score more than 95 percentile atleast.

Hope that helps!