Final answer:
The incorrect option in the rule of nines is D) Back - 9%, as the entire back should be assessed as 18% of the body area in an adult.
Step-by-step explanation:
When assessing the size of a burn using the rule of nines for an adult, the option that is not correct is D) Back - 9%. According to the rule of nines, specific parts of the body are associated with a percentage of body area. For an adult, the correct percentages are Arm - 9%, Leg - 18%, Head - 9%, and the entire Back - 18%. This method is crucial in guiding decisions made about the need for specialized treatment, as accurate assessment of burn size can significantly affect patient care.