Final answer:
The Registered Nurse (RN) is most responsible for the initial assessment and ongoing evaluation of client care, as they develop and monitor the patient's care plan.
Step-by-step explanation:
The most accountable individual for an initial assessment and the ongoing evaluation of client care in a healthcare setting is a) Registered Nurse (RN). The RN holds primary responsibility for conducting the initial nursing assessment and developing, implementing, and evaluating the care plan for patients. Physicians have a role in overseeing the medical aspects of patient care, but the coordinated, day-to-day evaluation and response to a patient's changing condition often falls under the purview of nurses. Nurse's aides can help in providing care and reporting changes to the RN, but they do not have the training to conduct assessments or manage care plans. Social workers may be involved in aspects of patient care, particularly related to social needs and discharge planning, but they do not have the responsibility for medical or nursing assessments.