if I absent during the 6th subject exam in class 11(school) and passed on the rest of all subjects so I have to give a re-exam of the 6th subject or it will consider a pass
It depends on the board and its regulations under which you are studying. In general the best of 5 is considered to be the passing criteria. So you can get passed until and unless your board doesn't permit this. If the board don't permit then you have to sit for a re-exam of the 6th subject.
I hope my answer helps. All the very best for your future endeavors!