Final answer:
The priority nursing intervention when a client presents unidentified pills is to ask if they have the original prescription bottle, as this will provide the necessary information for correct medication identification.
Step-by-step explanation:
When a client presents a nurse with a baggie of unidentified pills and is unsure of which medication they are taking for pain, the priority nursing intervention is to ensure the correct identification of the medication. The best option would be A. Ask the client if he or she has the bottle the drug was dispensed in from the pharmacy, as the original container would have the label with the medication name, dose, and prescribing information. This is crucial for patient safety and to prevent medication errors. Options such as notifying the healthcare provider, documenting the client's statement, and calling the pharmacy are also important, but the immediate priority is to identify the medication accurately.