Dear Anand

Yes you can definitely apply for NDA II Examination, however you should submit the proof of completing Class 12 before June 24, 2019.

You can check the Note 2 pertaining to your situation extracted from the Education Eligibility Criteria of NDA II 2018 notification dated June 6, 2018:

" Note 2: Those candidates who have yet to qualify in the 12th class or equivalent examination and are allowed to appear in the UPSC Examination should note that this is only a special concession given to them. They are required to submit proof of passing the 12th class or equivalent examination by the prescribed date (i.e. 24th June, 2019) and no request for extending this date will be entertained on the grounds of late conduct of Board/University Examination, delay in declaration of results or any other ground whatsoever."

Hope it helps! All the best!