Final answer:
Air flowing out of the lungs is known as expiration, which is a phase of pulmonary ventilation along with inspiration. Expiration occurs when the diaphragm relaxes, increasing lung pressure and expelling air. The correct option is 1.
Step-by-step explanation:
Air flowing out of the lungs is known as expiration. This biological process is one of the two main phases of pulmonary ventilation, which entails the movement of air into and out of the lungs. During expiration, air is expelled from the lungs as a result of the diaphragm and other respiratory muscles relaxing, increasing the pressure inside the lungs to be greater than the atmospheric pressure, thus forcing air out.
The counterpart to expiration is inspiration (or inhalation), wherein air is drawn into the lungs as the diaphragm contracts, creating a lower pressure inside the lungs compared to the atmospheric pressure. Expiration allows for the removal of carbon dioxide, a metabolic waste gas, from the body, thus playing a crucial role in maintaining the body's pH balance and facilitating effective gas exchange within the respiratory system. Hence, 1 is the correct option.