Final answer:
The evaluative action by the nurse is assessing a client's blood pressure after stress reduction techniques to determine the effectiveness of the intervention.
Step-by-step explanation:
The action by the nurse that best represents the evaluative portion of the nursing process is assessing a client's blood pressure after teaching stress reduction techniques. This step involves determining the effectiveness of the interventions performed, such as stress reduction techniques, by evaluating the client's outcome, which in this case would be any changes in blood pressure readings. Since the nursing process includes assessment, diagnosis, planning, implementation, and evaluation, it is critical to measure and compare blood pressure before and after the intervention to discern if there has been a positive effect.