NIOS is a recognised body. And so even if you pursue Science through NIOS, admission to MBBS or B.Sc should not be an issue. For example, if we take MBBS, admission to all Medical Colleges across India is through NEET. And to be eligible for NEET, you should complete your 12th with Physics, Chemistry, Biology and English as your core subjects. But there are students who do not have Biology in their 12th and such students can take up Biology as an additional subject from NIOS and still be eligible for NEET provided they score 50% in PhysIcs, Chemistry and Biology. It is 50% for General Category, 45% for PWD and 40% for OBC,SC,ST. So even if you take up Science from NIOS, you will be eligible for courses like MBBS, B.Sc.