Final answer:
The essential intervention during the working stage of a therapeutic relationship in nursing is implementing actions to achieve expected client outcomes.
Step-by-step explanation:
During the working stage of a therapeutic relationship between a nurse and a client with psychosocial needs, the intervention that is essential is B. Implement nursing actions that are designed to achieve expected client outcomes.
This phase involves actively working toward the goals established in the initial stages of the relationship. The nurse utilizes the interventions and strategies discussed with the health care team to support the client's current needs. This includes but is not limited to, education of staff and clients, direct patient care, and regularly assessing progress towards goals.