NDA

If you join NDA for Air Force and you have to go for flying branch only.

Checkout this Answer on Shiksha
https://ask.shiksha.com/how-can-i-join-nda-what-is-the-best-way-for-the-same-qna-4182280?referenceEntityId=4185170.

For NDA exams, your GK has to be strong, current affairs, reasoning & maths for the written exam. But besides GK, your Maths should be very strong as there will be separate paper for the Mathematics. For SSB interview overall personality development is required. You must focus on extempore, Group discussion, physical strengthening and other psychological tests as required for SSB interview.

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You will find best answer.

Continue studying your class 11th and class 12th Maths carefully. Revise all the NCERT Questions of the books. Get a preparation book for NDA Exam like Pathfinder by Arihant, Upkar, and other publications.

No, officially you can't, because eligibility criteria for NDA exam is that you should have passed class 12th class before the SSB interview, as you have to present class 12th marksheet during the time of SSB interview. But yes, if you meet the age requirement, you can apply for the written exam, and then you would not be able to appear for the SSB interview. Also, as the exam will include the syllabus of class 11th and class 12th, so there is no benefit of appearing in it now. So, you should appear after class 11th that too for the written only not SSB.

Best coaching of NDA is Minevera Academy and Major Khalsi Academy is also good.

Prateek, you should prepare for the NDA examination because you have a very good chance to qualify the NDA examination after completion of your 12 class.

Aspirants must have cleared class 12th examination or equivalent examination with Mathematics and Physics subjects from a recognized State Education Board/ University. So, you would not be eligible for NDA exam.

Hi Shreedam!
There are two ways; either through NDA entry or TES entry. You can find the details on this link http://joinindianarmy.nic.in/alpha/Intermediate.htm.