hi,

see the eligibility criteria for gate exam is candidates who have studied bachelor of technology of 4 years course or diploma + btech of 3 years course or msc course in relevant discipline or bachelors course of 4 years duration are eligible to apply. now final years students of graduation or post graduation are also eligible to appear in the exam. now coming to the backlog papers, you may appear in gate exam even if you have current backlog, but at the time of counselling or recruitment process through gate score, you must have the clear academics records and passed  your supplementary exam  as well as btech final exam.

hope you may understand.