Hey Chatur,

In order to appear as external candidate in your Class 12th board examination you will have to go for your Class 12th from open board like NIOS.

Also you can appear in Class 12th board examination of a regular board of education such as CBSE , ICSE and other state boards as a external candidate if you reappear in Class 12th board examination having not managed to secure marks as per your expectations and want to improve that.

So i hope this helps and all the very best to you!