What is the approximate surface area of the lungs when fully extended?

The approximate surface area of the lungs when fully extended is about 70 square meters. This expansive surface area is crucial for gas exchange, as it allows for a larger interface between the alveoli in the lungs and the capillaries where oxygen and carbon dioxide are exchanged.

When considering the physiology of the respiratory system, the alveoli are numerous and tiny, significantly increasing the total surface area relative to the volume of the lungs. This adaptation is essential for efficient respiratory function, enabling a higher rate of gas diffusion.

Although the values for surface area in the other options may seem plausible, they either overestimate or underestimate the actual surface area that would be available for gas exchange in a healthy adult. The figure of 70 square meters is a well-established estimate based on anatomical studies and physiological assessments, making it the most accurate choice among the options provided.