CBSE 12th

Use the Digilocker app, enter your Aadhar card details and retrieve Digilocker-verified marksheets, so you can use in counselling and admission procedure, same time apply for duplicate marksheet on CBSE website with procedure. You will get duplicate marksheet.
Don't worry.

First of all, for getting admission in NIT, you should have 75% as minimum marks. You need 5% more for eligibility to get NIT.

You can go for UPSC preparation. Most of the syllabus of UPSC is from humanities.

No (as per the last year's statistics). But many seats were left empty last year, so you may try to get a seat if you're lucky enough.

Since you are an aspirant of B.Tech in agriculture, you might not need coaching that much. Still, if you are planning to go to Kota then you might perform well and can also go for more good branches in many good colleges. But it's good that you have your goal clear. Work accordingly. Keep your spirit high.
All the best.

Yes, you can easily get admission in the 1st round.

To get admission in Anna University, you have to take "TANCET ". Apply for it and score good marks and get admission in Anna University. For more details, see the official website of Anna University.

One of my friends is in jet airways and she also passed out from frankinn I believe.