Final answer:
The client who denies any memory of a traumatic event they experienced is using dissociation as a defense mechanism. Dissociation involves mental separation from distressing experiences, which is distinct from other forms of expressing or managing stress.
Step-by-step explanation:
A nurse at a mental health clinic should recognize that a client who denies any memory of a traumatic event they experienced is using dissociation as a defense mechanism. Dissociation is a process where a person mentally separates themselves from the reality of a painful or traumatic experience. Among the four options presented, denial of a traumatic event (option b) is a classic example of dissociation, where the individual's mind unconsciously pushes away distressing memories to protect itself. This is different from openly talking about fears and anxieties, expressing anger during therapy, or practicing relaxation techniques, none of which involve the mental separation from experiences that characterizes dissociation.