Science

Yes, you'll be eligible to take entrance. Just at the time of admission, you're supposed to show the Gap year affidavit.

Hard to tell. As the cut-off gets quite high. But as you fall under a category, you can hope. Thanks.

Yes, you can do that but your rank matters.

Of course. Every college accepts NIOS degree. Its a government of India recognised degree so be hazzle free. You can easily get seat. Nobody can deny your degree. If someone denies also you can just register a case against him/her. NIOS degree has its own value. Thanks.

Unfortunately, Cochin University do not offer any undergraduate programme in marine biology. Please check the link for more info:
http://cusat.ac.in/dept.php?deptcode=marinebio

Hi Abhishek,
For M.Sc Biotechnology, you can go for Punjab University, Delhi University. The admission is based on the entrance exam, and the syllabus is what you have studied in your graduation. Also, you can visit their official site for syllabus and admission procedure. As there are limited seats

So far my knowledge goes, you can pursue M.Sc Math in some Institute after doing B.Tech Mechanical. For example, Chennai Mathematical Institute allows B.Tech /BE for doing M.Sc Math. They also allow B.Sc Math/B.Math/B.Stat. For M.Sc Maths, you can visit their site for confirmation. Best wishes.

At first, you will be studying the very basic and dominated by what you have already studied in class 11th and class 12th. So, you can actually do both, but hard work is obviously required here. Also, time management is very important.