Final answer:
The charge nurse should address the nurse's unethical behavior and ensure the client's safety. Education and support for the staff nurse are also important.
Step-by-step explanation:
The priority action for the charge nurse in this situation is to address the nurse's unethical behavior and ensure that appropriate actions are taken to protect the client's safety and well-being. Giving a placebo medication and misleading the client is a violation of ethical principles and can harm the trust between the nurse and client. The charge nurse should confront the staff nurse about the incident, gather all the necessary information, and report it to the appropriate authorities. Additionally, the charge nurse should provide education and support for the staff nurse regarding appropriate behavior and handling of medication.