Final answer:
Registered Nurses and Registered Practical Nurses can perform the controlled act of administering medication, which is part of their scope of practice, especially when providing treatments like dialysis.
Step-by-step explanation:
The actions that fall under the controlled acts that Registered Nurses (RNs) and Registered Practical Nurses (RPNs) can perform include administering medication. This is a core part of their scope of practice. RNs and RPNs work with a focus on providing specialized treatments like dialysis treatments, which requires careful monitoring of patient vital signs and preparation of solutions and equipment to ensure procedures are accurate and sterile. Diagnosing medical conditions, however, is typically outside the scope of practice for RNs and RPNs unless they have additional qualifications. Therefore, the correct answer to the question is 'a. Administering medication'.