Which of the following can lead to respiratory acidosis?

Pneumonia can lead to respiratory acidosis due to its impact on the lungs and gas exchange. In pneumonia, the alveoli, which are responsible for the exchange of oxygen and carbon dioxide, become inflamed and filled with fluid or pus. This reduces the lungs' ability to effectively remove carbon dioxide from the bloodstream. As carbon dioxide levels build up, they lead to an increase in carbonic acid, resulting in a decrease in blood pH, which characterizes respiratory acidosis.

In contrast, anemia primarily affects the oxygen-carrying capacity of the blood rather than the respiratory function directly. Hyperventilation typically results in respiratory alkalosis due to decreased carbon dioxide levels in the blood. Anaphylaxis involves severe allergic reactions that can lead to respiratory distress but does not directly cause respiratory acidosis unless it severely impacts breathing efficacy.