B.Sc

No. The answer is obviously a no. You'll have to start from the very starting.

Did you mean you want to pursue Maths (Hons) in post graduation? If yes, then you will have to appear for entrance test of every government institute you want to take admission in. If you want to go in IIT you will have to appear for IIT JAM. If you want to go fir research in your subject along with post graduation you can apply for TIFR. For private colleges, there arena't any entrance tests.

Yes, of course, you can get admission in maths hons in Delhi University at least and other state Universities too. There may a little deduction in your percentage though while calculating for best 4.

If you are really determined or really want to take admission in renowned government institute like Delhi University, you can drop a year. But that according to me will be wastage of time. You can take admission in state University. They will surely provide you admission. State Universities like MDU or KU will definitely provide you admission. In case you go for dropping a year, you can also prepare for IIT-JEE.

You can go for M.Sc. in any of the above subjects. For that, you will have to take entrance test. Institutions like IITs provide admissions on the basis of IIT JAM result. Option for civil services is always there. You can take SSC CGL exams. If you have good teaching skills, you can apply for coaching institutes like ALLEN or Akash.

Admission to B.Sc. in Nautical Science from Indian Maritime University, Chennai- Mumbai, T.S.Chanakya Campus is through counseling based on the rank obtained in Indian Maritime University Common Entrance Test (IMU-CET).
Important preparation tips for IMU-CET:
Initially start studying for as long as you can & gradually increase your study hours.
Check out the Syllabus given to you for IMU CET 2018 entrance exam.
Make short notes & revise them before your exams.
For the purpose of General Knowledge, keep a track of the latest news through newspapers & television media.
Regards.

Almost every institute in India gives admissions for graduation on the basis of 12th marks. So, do well in your boards. If you want to go for research, you can take admission in IISC, Bangalore. Admissions there are given on the basis of IIT-JEE result.

Following is the link where you can check the best colleges in B.Sc. Computer Science according to your elegibility
https://www.shiksha.com/science/colleges/colleges-Mumbai?sp[]=107.

The weightage for selection is 60% for CAT, 25% for PI & 15% WAT. You have fair chances of selection. Prepare yourself for WAT-PI with a good SOP.

Hi Sayak!
You can find all the details including admission and eligibility by following this link https://www.shiksha.com/mass-communication-media/course/b-sc-hons-in-mass-communication-and-videography-st-xavier-s-college-park-street-kolkata-83779.