Final answer:
The nurse was testing the glossopharyngeal nerve, which is responsible for taste, salivation, and the gag reflex associated with the posterior oral cavity.
Step-by-step explanation:
The nurse was testing the glossopharyngeal nerve in the scenario described. This cranial nerve is responsible for taste as well as salivation in the anterior oral cavity, as well as triggering the gag reflex when the back of the throat (oropharynx) is stimulated. During a cranial nerve exam, testing this nerve involves both sensory and motor components: the taste sensation in the posterior one-third of the tongue and the ability to elicit a gag reflex.
If the nurse is evaluating the taste sensation, the correct answer would be the facial nerve (CN VII), which handles taste in the anterior two-thirds of the tongue. However, if the nurse is testing the gag reflex or salivation from the parotid gland, the correct answer would be the glossopharyngeal nerve (CN IX).