In the absence of surfactants:

A. A collection of excess fluid within the intrapleural: This describes a pleural effusion, not orthopnea.

B. Difficulty in breathing that is relieved by sitting upright: This is the definition of orthopnea, commonly seen in conditions like heart failure.

C. A bluish color of the skin induced by hypoxemia: This describes cyanosis, not orthopnea.

D. A lung infection like pneumonia: Pneumonia is a specific infection, not a description of breathing difficulty in certain positions.

A. There are fewer alveoli available for gas exchange: Pneumonia causes inflammation and fluid buildup in the lungs, while collapsed alveoli (atelectasis) reduce the surface area available for gas exchange. This results in impaired oxygen absorption and carbon dioxide removal, making breathing less efficient.

B. Rapid shallow breathing can compensate for the collapsed alveoli, no further treatment is required: While rapid, shallow breathing can be a response to decreased oxygen levels, it does not fully compensate for the loss of functional alveoli. Patients with pneumonia and atelectasis often require medical intervention, such as oxygen therapy or breathing exercises, to improve lung function.

C. O₂ levels in the blood will increase: Oxygen levels in the blood decrease, not increase, because fewer alveoli are available to facilitate gas exchange. The impaired alveolar function leads to hypoxemia (low blood oxygen), which can cause symptoms like shortness of breath and cyanosis.

D. There will be no effect on breathing and O₂ levels in the blood: Pneumonia and collapsed alveoli significantly affect breathing and oxygen levels. Patients may experience difficulty breathing, reduced oxygen saturation, and increased respiratory effort as their bodies try to compensate for poor oxygen exchange.