Final answer:
The organ located at #4 and #9 is the Alveoli, which are tiny air sacs in the lungs where gas exchange occurs.
Step-by-step explanation:
The organ located at position numbers #4 and #9 is the Alveoli. The alveoli are tiny air sacs within the lungs where gas exchange occurs. The alveoli are at the end of the respiratory tree and are arranged in clusters throughout the lungs. According to the proper order of airflow during inhalation, air first enters the respiratory system via the nasal cavity, passes the pharynx and larynx, then travels down the trachea, into the bronchi and bronchioles, before finally reaching the alveoli.
Item #9 in the list provided represents the alveoli, as it is the last structure encountered by air entering the body.