Question

When a person blames a situation entirely on someone else, he or she may be using the defense mechanism known as _____. projection reaction formation regression denial

Answer 1

Denial project reaction

Answer 2

The answer is: Denial.
Example:
Person 1: "Are you the one responsible for this mess?
Person 2: No, it wasn't me, it was him, all him! Believe me, it was not me!"

Person 2 is denying any involvement in the situation.

Hope this helps.