Who is creating this mess?

The correct answer is D. By whom is this mess being created?

A. Who has created this mess? is in the past tense, while the question is about the present.
B. By whom has this mess been created? is also in the past tense.
C. By whom this mess is being created? is grammatically incorrect.

D. By whom is this mess being created? is in the present tense and is the only option that makes sense in the context of the question.

The question is asking who is currently creating the mess. The answer is the person or people who are currently making the mess.