Hey,

The cut offs do change every year for IIT JAM.
The qualifying marks In IIT JAM exam be 27 for MSC Chemistry. For you subject as chemistry this year the closing rank for first round is AIR 305. For the third round it is 318 i.e there is not much difference in the first and the final round. For opening and closing ranks of other IITs you may look for the below link

Https://jam.iitkgp.ac.in/

Hope this helps.