A mark lower than 40 means there is no chance to get into even NITs however tough be the exam
Usually GATE cutoff is around 25 marks, but clearing the cutoff do not mean anything
To be safe to get into IIT, one has to prepare to get 70+ marks out of 100
A general category student needs a rank around 200 for IIT direct admission. For more details about colleges and last ranks, see here Top colleges after GATE