Hi,

Well there are usually two types of students. One who have six subjects in class 12th and the other who have five subjects. The ones having five subjects need to pass in all five subjects to move ahead as per cbse, I guess. For students with six subjects also passing in five is needed. So, if a student with six subjects passes in only four then he or she will have to take supplementary paper for one more main subject to pass in it cause as per the cbse say.

I hope my answer helps.

All the best.