B.Tech

You will get several suggestion on choosing the branch, but you should depend on your interest and choose accordingly. In my opinion CE has good scope due to Digitalization. I would suggest you with one good college to provide this course I.e. UEM Kolkata and have good placement. To know more about

You are advised to appear for GATE and do M.Tech in the area of your interest to take up technical career. As you have not shared your branch specific advice can not be shared.

No, they can't take your 12th or 10th mark-sheet they just say you to take all these original documents so that they can verify that the certificate and marks mentioned by you at the time of applying is correct or not.

B.Tech biotechnology is good among all of the following course mentioned by you and it has good scope in future so don't worry about jobs if you studied well then you get a job easily.
All the best!

If you are interested in B.Tech food technology then you may join the college as many students are taking EE so there is more crowd and less job but if you are doing B.Tech food technology then it has less crowd and more jobs so you join food technology course.
All The Best.

Numerous Government as well as private job opportunities exist in front of EC Engineers! Pursuing Masters course will help one in taking up teaching job!
Talking about Government sector, some of the well known recruiters are-
BHEL
BEL
BSNL
DRDO
Indian Armed Forces
HAL
ISRO
ONGC
Government Airlines and so