does nios mention in their 12th board certificate any sort of information that states that i m failed from 12th cbse and that this certificate was an improvement exam
Hii!
You don't need to worry on this problem. There is no mention as such in the marksheets of students issued by NIOS, that he/ she failed CBSE class 12th and this is an improvement exam result. You get a normal marksheet and result as other students do. So, don't worry.
Hope this helps.
Good luck!