Final answer:
The correct choice for objective data is 'unable to palpate femoral pulse in left leg', as it is a measurable fact observed by the nurse, and not based on the patient's subjective feelings.
Step-by-step explanation:
The question asks which option is considered objective data in the assessment of a teenager admitted to the emergency department. Among the options given, "unable to palpate femoral pulse in left leg" is the correct choice as objective data. This is because it is a fact that can be observed and measured by the nurse, unlike the other options that are based on the patient’s subjective experience of pain and discomfort. Objective data are vital in forming a baseline for treating trauma in the nervous system and other medical conditions.