JEE Mains is the entrance examination for pursuing B.E and B.Tech. It is also for studying B.Arch. These courses are offered at Private Engineering Colleges, Government Run Engineering Colleges, NITs, IIITs and CFTIs. This is not for B.Sc. For B.Sc, the admission is based on the Institution's guidelines as to whether it accepts Merit based admissions or conducts its own entrance examination.To qualify for JEE Mains, there is no minimum aggregate criteria. But if you want to join NITs, IIITs or CFTIs then you should score a minimum aggregate of 75% only in your 12th. 11th marks aren't considered. And then to appear for JEE Advanced which is the gateway for admission to IITs, you will need to fulfill the 75% aggregate condition. Now it is 75% for General Category and 65% for Reserved Categories. So how much you score in 12th is what matters to secure your eligibility for NITs, IIITs, CFTIs and JEE Advanced.