CBSE 12th

You can do B.Sc. in gaming.

B.Tech or BE is best, if you are not interested in this, then biotechnology is also very good field. Otherwise, you can try for mathematics and computing in DTU. Engineering physics is also good.

You need to get 90% in general category.

It depends on your interest. If you are interested in humanities, you can go for that and after class 12th, you can try to crack civil services exams.
Good luck.

She can either pursue B.Sc in geology or B.Sc in earth science. This field is still in an infant stage in India, but according to experts this field will have a great scope in India in future. Geologists and earth scientists are in great demand in Australia and New Zealand. So, if she is really interested in this field, there is nothing better than becoming a geologist.

Yes, you class 12th percentage do matter, a minimum of 75% is needed to crack IIT JEE advanced. Other entrance exams do have eligibility criteria of around 60%.

First, you have to register and take admission tests like SAT, ACT TOEFL or IELTS and you have to do really well in these tests, if you are particularly aiming for IVY Leagues.
You have to check the university's website, if they require SAT subject test. You can collect your class 9th, 10th, 11th and 12th grades and SOPs and LORs. The university will also look at your achievements and extra-curricular and finally you can apply to universities of your choice.

Yes, it is. Are you looking for merchant navy or Indian navy? If you get selected for Indian Navy, then it will give you a stable job with lots of adventure. It brings in a lot of prestige also.
Merchant navy enables you to earn a lot of money and visit many countries. Having said so a career in navy means staying away from family for long time and being cut off from shores for days. If that suits you, then there are no reasons why you should not opt for it.

Any student can change his stream to humanities after XII board. You are advised to review detailed eligibility criteria of targeted universities where you intend doing graduation degree in humanities.