Final answer:
The objective datum in the SOAP format is the patient's incision site appearing clean without any purulent drainage or erythema, which is an observable and measurable fact.
Step-by-step explanation:
The objective datum from the nurse's assessment in SOAP (subjective data, objective data, assessment, and plan) format is: "The patient's incision site looks clean without any purulent drainage or erythema." This is considered objective data because it refers to measurable, observable, and verifiable information that the nurse can assess directly through her senses. Subjective data is information based on the patient's feelings, perceptions, and self-reported symptoms, like the patient stating they have no pain. Plans for care, such as changing dressings or administering antibiotics, are not considered objective data but are part of the plan of care.