Final answer:
Respiratory acidosis occurs when the lungs are unable to remove enough CO2 on expiration, leading to an excess of carbonic acid in the blood. This can happen due to certain conditions that interfere with respiration, such as pneumonia or congestive heart failure.
Step-by-step explanation:
Respiratory acidosis occurs when the blood is overly acidic due to an excess of carbonic acid, resulting from too much CO₂ in the blood. This can happen when the lungs are unable to remove enough CO₂ on expiration. Conditions like pneumonia, emphysema, or congestive heart failure can interfere with respiration and lead to respiratory acidosis.