Which gas is typically associated with increased lung ventilation when its levels rise?

The correct choice is Carbon Dioxide. In the human body, the levels of carbon dioxide are crucial in maintaining respiratory function. When carbon dioxide levels rise in the bloodstream, it leads to an increase in the acidity of the blood. This condition, known as hypercapnia, triggers chemoreceptors in the body, specifically in the medulla oblongata, to signal the respiratory system to increase ventilation. This response enhances the expulsion of carbon dioxide and helps restore normal levels.

Oxygen does play a vital role in the respiratory process, but it does not directly stimulate ventilation in the same way carbon dioxide does. The body is more focused on maintaining carbon dioxide levels, as they are tightly regulated, whereas oxygen levels do not trigger significant changes in ventilation until they drop to critically low levels. Nitrogen does not significantly affect ventilation as it is a relatively inert gas in the respiratory context, and methane is not a typical component of the gases involved in human respiration. Thus, carbon dioxide is the key gas associated with increased lung ventilation in response to elevated levels.