Final answer:
Oxygen (O₂) has the greatest effect in controlling lung ventilation as it is responsible for oxygenating the blood and delivering oxygen to the body's cells. Carbon dioxide (CO₂) is a waste product that is exhaled during ventilation.
Step-by-step explanation:
Oxygen (O₂) has the greatest effect in controlling lung ventilation. During inhalation, oxygen enters the alveoli through the respiratory system and diffuses into the bloodstream. This oxygen-rich blood is then transported to the body's cells, where it is used in cellular respiration. Carbon dioxide (CO₂), on the other hand, is a waste product of cellular respiration and is exhale during the process of ventilation.