CBSE 12th

Dear Rajendra,
You can do Bachelors in prosthetics & orthotics course from Chennai.

No. PU doesn't offer automobile and for other branches, it offers only on JEE Mains rank.

You may apply for a Diploma offered by many institutes like Frankfinn, IATA, etc. through their websites or in person. Choose from here:
https://hospitality.shiksha.com/diploma-in-cabin-crew-training-in-india-categorypage-6-87-271-0-0-1-1-2-none-1-0

Any graduate who has passed or appearing for the final year 3 years graduation degree examination in any discipline (Science, Commerce, Arts, Engineering or any approved University) is eligible to apply for admission in MCA postgraduate degree course. Candidates must have mathematics as a subject in their 10+2 course or any one year of graduation degree.
You are not eligible for seeking admission in MCA no. You are advised to choose any graduation degree of your choose and appear for MCA entrance examination in final year of graduation degree.

You may refer to the answer below for better clarity-
https://ask.shiksha.com/how-to-apply-for-pilot-after-class-12th-qna-3590531

After 12th Arts, there are many options to be pursued like B.A., L.L.B., B.B.A.,B.com,C.A. graduate and others. But choice depends on you to select from many of these.

Hard work, self-study and practice should be your 3 mantras to score 95% or above in class 12th.
Good luck!

IITs are the best institutes for engineering in India. You must target IIT-JEE Mains/Advanced. Apart from IITs, NITs are the next best. NIT-Jaipur, Warangal, Trichy, Bhopal, Surat are some of the best. Among private institutes, VIT-Vellore, BITS-Pilani/Mesra are reputed ones. Other government institutes are IIST-Trivandrum, IISER Bhopal/Pune/Bhubaneswar.

There are very few colleges offering 100% placement and they include:
IIM, Indore
Nirma University, Ahmadabad
There aren't any more credible institutes for this course. And, anyway it does not matter. If you do integrated BBA and MBA, it will take 5-years and the course fee will be very high and instead if you do 3-years BBA or BMS from a good state university affiliated colleges such as St Xavier's, KJ Somaiya, NM in Mumbai that will cost hardly 1 Lac including everything.Further, you will have more options for MBA later.