What condition is characterized by alveoli filled with fluid?

The condition characterized by alveoli filled with fluid is pneumonia. Pneumonia is an infection or inflammation of the alveoli in the lungs, which can be caused by bacteria, viruses, fungi, or other pathogens. In this condition, the alveoli become inflamed and are often filled with fluid or pus, which can impair gas exchange and lead to symptoms such as cough, fever, and difficulty breathing. This fluid buildup reduces the surface area available for oxygen absorption and carbon dioxide expulsion, significantly affecting respiratory function.

Other conditions listed do not typically involve this specific accumulation of fluid in the alveoli. Pneumothorax refers to the presence of air in the pleural space, leading to lung collapse. Chronic bronchitis involves inflammation of the bronchial tubes, which results in a productive cough but does not fill the alveoli with fluid. Asthma is characterized by airway constriction and inflammation but does not specifically involve the accumulation of fluid in the alveoli. Hence, pneumonia is the most accurate choice when describing the filling of alveoli with fluid.