Which action is appropriate for a nurse caring for an older adult found outside during a snowstorm?

Obtaining a rectal temperature is particularly appropriate in this scenario because it provides the most accurate measurement of core body temperature, which is crucial for assessing hypothermia or other temperature-related conditions. Older adults are at higher risk for hypothermia, especially when exposed to cold weather conditions such as a snowstorm. Understanding their core temperature allows the nurse to determine the severity of the situation and initiate appropriate interventions, such as rewarming procedures, if necessary.

In contrast, while identifying the client, determining allergies, or administering oxygen may be important in other contexts, they are not immediate priorities in this specific situation where hypothermia is a significant concern. Administering oxygen would generally be reserved for patients showing signs of respiratory distress, and ascertaining allergies or asking for identification doesn't address the immediate health risks posed by exposure to extreme cold. Thus, focusing on the assessment of temperature directly relates to the critical need for rapid evaluation and intervention in an emergency involving exposure to severe cold weather.