Final answer:
Due to the increase in demand for healthcare services and an aging population, RNs comprise a significant portion of the healthcare workforce. Without explicit data, the exact percentage cannot be ascertained, but it is typically known that they form one of the largest groups among healthcare professionals.
Step-by-step explanation:
Registered Nurses (RNs) form the largest group of health care professionals in the US. To answer the question, let's turn our attention to the demand side, driven by an aging population and the expansion of healthcare coverage through legislation, which abundantly increases the number of patients requiring care. Due to the lack of exact statistical data within the provided information, I'm unable to definitively select an option between one-fourth, one-third, one-half, or two-thirds. However, it is common knowledge that RNs represent a substantial percentage of the healthcare workforce, making nursing one of the largest health care professional groups.
The labor market for nurses and other healthcare professionals is poised to face several challenges. With the increased demand for healthcare services, especially nurses, economics and labor market studies predict significant impacts on supply and demand. While the exact proportion of RNs compared to all healthcare professionals wasn't provided, one can infer that they represent a very significant share of the health care labor force. For the most accurate answer, one should refer to the latest statistical data from a reputable source such as the Bureau of Labor Statistics or industry reports.