CBSE 12th

Hi Ganta, you must take the SAT or ACT to be eligible for admission in any US University, Harvard University which you are asking about is one of the world's top most and very selective.Your academic percentage is very good, but they will also see your extra curricular activities.First decide what you want to study, check Harvard website and kind of students they admit. The fee can be around $60000 or more per year.If you prepare well there is always a place for deserving students and you can take education loans or get scholarships.

Hi,
It is a deferred program which leads to MBA, you must apply to the 2+2 program during the final year of your Bachelor's degree. Since you have lots of time now you can build your profile and make yourself fit for Harvard. Check the eligibility here:
http://www.hbs.edu/mba/admissions/application-process/Pages/student-applicants.aspx

Hi Supreet,
Yes, you can. You can also apply to a top university on the basis of your class 12th percentage.

No need to take any exams, just score well as they will select you.

Yes, you can join with 10+2 marks greater than 55% in mathematics, physics and English.

Hi Abhi,
To become a certified ethical hacker you need to take a separate course on ethical hacking and you may get certified by EC Council followed by exam.
It's a good to see that you have set your objective in your early days and I assume you want to settle your career in IT security. If yes, then choose your graduation with specialization as Security. It would help you to understand the security domain and it's application and how EH skills would help you along it's way.

Hello Sneha,
Yes, you can pursue archeology. It's very typical subject but great possibilities.
Best wishes.

Hello Vignesh,
You have already chosen a very good way for your bright future. You can go for CA or take up one of the various Specialization available after B.Com.
Best wishes.

Hello Sanjay,
Frankly, I have not understood your query. You are already doing a job for three years after the completion of Diploma.
You have to decide about your future. You can take a break from the job and go for graduation in fire &safety. You can continue in the same job. But, what's your passion? I would advise you to follow your passion.