Dear aspirant, there is an eligibility criteria for the IIT JAM exam, it requires a minimum of 55% marks for UR/OBC category and 50% for PWD/SC/ST category in bachelors degree along with essential subjects in it with minimum duration for the subject.For detailed information regarding the subjects and eligibility you may refer o the link below:

https://university.careers360.com/articles/jam-eligibility-criteria

Hope it helps.

All the best:)