Which of the following conditions is characterized by the collapse of a part or all of a lung?
Asthma
Pneumonia
Pulmonary embolism
Atelectasis
Atelectasis refers to the collapse of a part or all of a lung. It occurs when the alveoli (air sacs) within the lung become deflated or collapse, leading to incomplete or no air exchange in that area. This condition can be caused by various factors, such as blockage of the air passages (obstructive atelectasis), compression of the lung tissue (compressive atelectasis), or surfactant deficiency.
Hence, the correct answer is option 4.