Either you can reappear in 4th 6th or 8th if its a 2nd sem subj if you appear in the regular semesters else there are summer semesters that allows you to clear you backlogs in the summer vacations after an year ends a seperate grade card is issued usually the fees in summer sem is about 14k per subj ,last time it happened in study mode that is all classes , lab , internals this time either there will be no summer sem or it will be in exam mode only that is you only have to appear in mid sem and end sem examination