The variants of asking a question

"Which topic did you write your article about?"

"About which topic did you write your article?"

"Which topic you wrote your article about?"

Which of these variants would be correct for writing? My take is that the first question is right in every situation, and the second and third are acceptable only in informal speech. I know that the rule says that there is the single correct construction of wh- questions, but I am wondering if there are any other ways of asking a question.