CBSE 12th

Alongwith your graduation you can also go for the course of ethical hacking as nowadays companies higher ethical hackers for safeguarding their data and websites. Wish you luck.

No,it is not necessary to study maths in class 12 th. You are also eligible if you have studied biology in your class 11th and 12 th along with physics and chemistry.

You must have a capacity for hard work. In Science, chances do not come automatically, with a qualification. You have to show Research output and hard work. Your publications count a lot.
So, the conclusion is that you have to assess your hard work and your general intelligence.

You can do B.Sc non medical.

I don't think you will receive GDPI call from IIMs with 82 percentile in CAT. You will have to do really well and score atleast 99.5 percentile to get GDPI calls from atleast few older IIMs. Please understand that on an average 2 lakh students appear for CAT and 82 percentile means there are 36,000 students who have scored more marks than you. Seats in all IIMs combined is not more than 2000.

It would totally depend on your preferences. First year courses are compulsory courses and in second year you have option to pick electives and decide on which subjects you want to study. The options available to you include Human Resource, IT, Finance, Marketing, Organization Behavior, Strategy, Operations etc. Based on your preferences you can pick subjects in second year.

Go for Delhi University.

no not at all.