CBSE

No, Schools does not start teaching for 11 before class 10 results.

For getting admission in BA(hons) in Hindi from JHC, you must have 51 % in your class 12th.

It's difficult for you to get admission in Symbiosis college og arts and commerce, Pune, because there required percentage in 72% at least but you can apply once, they might give you chance, and give you admission in there college.

Yes it's totally acceptable. Check the criteria as per college and university.

No, you can't take admission in Ravenshaw University, if you have failed the accountancy exam because it is a core subject and if you fail in it, you won't be eligible for admission in Ravenshaw University.

Absolutely,
Your 10th 12th marks does not have guarantee with you being successful or even you getting placed on the basis of these results. However, some companies do ask for this criteria but always remember that these marks aren't going to help you in long run. What is going to help you is your skillset. So rather than to think about why you got so less marks try and build up more skills which will help you during interviews in IT sector.

TS Grewal is the best preference book for CBSE class 11th. You can pursue it for your better results.