Science

Yes, if you are interested in the A.M.E. Course, it is an undergraduate programme related to the maintenance, repair, and solving of the problems of an aircraft. Aircraft Maintenance Engineer is responsible for keeping the aircraft in airworthy condition. The eligibility criteria in B.Sc. A.M.E. Is Candidate must pass or appear 10+2 with Physics Chemistry and Mathematics (PCM). A.M.E. B.Sc. Is a 3 years course to get the best colleges of Aircraft Maintenance Engineering interested can attend national level entrance exam of A.M.E. CET.

As far as I am aware, yes there is a possibility.

Admission to the second year of Diploma is not feasible.

Eligibility criteria for the post-Higher Secondary Certificate (HSC) Diploma course is an HSC pass certificate. You are eligible to seek admission in Diploma course from a Polytechnic. Legally it is permissible to do Diploma and degree simultaneously. You can not pursue two degrees simultaneously from same or different universities. You are advised to evaluate whether you can handle simultaneous studies load of two courses and challenges in case of conflicts in time table, examinations etc.

HI Manisha,
You don't need to appear for any entrance exam. Although, different colleges and universities conduct their own admission tests for B.Com.

It totally depends on your interest. If you want to have a career in management then opt for BBA, otherwise you can go for BCA.

Which particular subject?

Commerce students are not eligible for B.Sc.

As your rank is quite good, so there is possibility that you can get admission.