CBSE

The JEE Mains exam syllabus consists of the topics from class 11th and 12th. Although, class 12th has more weightage in JEE Mains exam. Generally, it has 40:60 ratio. 40% for class 11th and 60% for class 12th.
So, if you will prepare only for class 12th, you will be able to score around 120 marks in the exam. But to score good marks, you should prepare class 11th class as well.

You can appear for VITEE/KITEE/SRMJEE/State Entrance Exam of your state. Also, just give the JEE Mains (as it will help you to take admission in various colleges of India). If you get good marks and you think you can get CSE in your rank, then its fine, else see your ranks in VITEE/SRMJEE/State Entrance Exam of your state and see if you are getting CSE branch. If you do not get a satisfying rank, you can give a year drop and prepare for JEE Mains and advanced, but please don't skip the JEE Mains, as I have stated the reason earlier.

Hi Kritika, NCERT books by far are the most popular and recommended.

Hi Shubhank, please enquire the same with your school authorities. There might be a possibility, but it won't be easy.

Hi,
Eligibility: Candidate must have passed 10+2 from a recognized board.
Admission Process:
Register and Apply: Interested candidates can apply online with the required information.
Merit Screening: Admission is based on the marks obtained in 10+2.
https://www.shiksha.com/bba/course/bachelor-of-business-administration-madras-christian-college-tambaram-sanatorium-chennai-110316

Yes, you can easily score 80+. Just keep practicing the numerical and revise the concepts. Solve previous years papers fully. Analyse the way questions are asked and try writing appropriate answers. Always use graphs/diagrams where ever possible. Best of luck.