Which is the right way to phrase "Who made this mess?" in the passive voice?
By whom were made this mess?
or
Who was this mess made by?
How should I write questions in passive voice?
Which is the right way to phrase "Who made this mess?" in the passive voice?
By whom were made this mess?
or
Who was this mess made by?
How should I write questions in passive voice?
Both This mess was made by who(m)?
and your second sentence Who was this mess made by? are correct.
Your first sentence is not grammatical. You can say By whom was this mess made?
Who made this mess? We normally change such interrogative sentences in the passive voice in the following two ways:
1- Who was this mess made by?
2- By whom was this mess made?
As we know whom is not very often used in spoken English as compared to who that is more natural and common both in spoken and written English, I prefer the first sentence in spoken English and the second one in formal English.