Final answer:
The narrowest portion of the adult airway is the cricoid cartilage.
Step-by-step explanation:
The cricoid cartilage is a firm, ring-shaped structure located in the trachea, specifically in the region just below the thyroid cartilage in the neck. It is one of the cartilages that make up the larynx, also known as the voice box.
The narrowest portion of the adult airway is the cricoid cartilage. The cricoid cartilage is a ring of cartilage with a wide posterior region and a thinner anterior region. It is attached to the esophagus and acts as a funnel-like structure that directs air into the trachea.