CBSE 12th

You can easily take admission in Amity University, Mumbai, but you have to appear for Amity JEE. Also, the minimum eligiblity criteria for admission in various courses is a minimum of 50% in board exams. Please visit this link for more details on various courses offered by Amity, Mumbai.
https://www.google.com/amp/s/www.shiksha.com/university/amp/amity-university-mumbai-46905

Hi,
As you have scored 70.2% in class 12th, so you are eligible to take admission in Delhi University. Nevertheless, as you know the cut offs are very high in du, so it will be difficult to get admission. However, you must give a try, fill up the registration form and see what is the status after third round.

Yes, you can apply for IIIT-Delhi. Your marks are too good.

As you have already appeared for class 12th board exams in the year 2018 and the improvement exam in the year 2019, you can no longer appear for more improvement exams. Also, a student can give the improvement exam only once that also in the succeeding year of their board exams.

Yes, your class 12th marks would be considered for any graduation course. But how much weightage the college gives would depend on various factors.

The eligibility criteria for admission at Vaish College of Law for BA LLB is "the candidate should 45% Marks (42.75% Mark in case of SC/ST Candidates) in 10+2 or any other equivalent examination from any recognized board".
The total fee for the course is Rs 1.6 lakhs.
Mode: Full-time
Duration: 5-years
Offered by: Maharshi Dayanand University, Rohtak
Bachelor of Legislative Law (LLB) honours is a five-year full-time Integrated programme in law offered by Maharshi Dayanand University, Rohtak with the approval of Bar Council of India (BCI).

No, there is no chance for you getting admission into M.Sc chemistry in the college mentioned by you with the above secured marks. You can apply for entrance exams and try to crack them to get a job or study further.

Yes, definitely your JEE Mains percentile is pretty decent to help you get admission into the top colleges in Tamil Nadu.
All the best.

In class 12th as there is an option for a student to opt for more than 6 subjects, the best 5 subjects are only taken for determining your percentage scored.
All the best.

It's not a problem. While your graduation course you will be taught all the things. As you have not studied computer so you will struggle a bit. But it's okay. You have to work hard from the first year.