Which of the following separates the lungs?

The mediastinum is the correct answer because it is the central compartment of the thoracic cavity located between the two lungs. This anatomical space contains important structures such as the heart, great blood vessels, trachea, esophagus, and thymus gland. It effectively separates the left lung from the right lung, allowing for independent movement and function of each lung during respiration.

The pericardial cavity, while important as it surrounds the heart, is contained within the mediastinum and does not act as a separator for the lungs themselves. The abdominal cavity, located below the diaphragm, houses organs such as the stomach, liver, and intestines, and is not relevant to the separation of the lungs. The pleural cavity refers to the space between the layers of pleura that surround each lung, allowing for lung expansion and contraction but does not separate the lungs from each other.