I fail in class 12 then I appear as privet candidate then is it written that I was failed previous year
Yes your result will show that you had fail and giving exam again as a private candidate.It will be known that you have cleared it in a second attempt itself.
I hope this helps
Yes it shall appear that you have given improvement exam and scores after Improvements exam will be considered.
Either ways you can give improvement exam in succeeding year of 12th attempt so in thatcase colleges will identify that you have renewed marksheet.