Which gas is primarily dangerous due to prolonged exposure in poorly ventilated basements?

Radon is primarily dangerous due to prolonged exposure in poorly ventilated spaces, such as basements, because it is a colorless, odorless, and tasteless radioactive gas that originates from the natural decay of uranium in soil and rock. When radon accumulates in confined areas, particularly in homes with basements or lower levels that are poorly ventilated, it can reach significant concentrations. Prolonged exposure to radon is a known risk factor for lung cancer, as its radioactive particles can be inhaled and damage lung tissue. Due to its properties and the common conditions under which it accumulates, radon is a significant concern in indoor air quality, particularly in regions with higher natural uranium content in the ground.

The other gases listed, while potentially harmful in certain contexts, do not have the same risk profile associated with prolonged exposure in confined spaces. For instance, carbon dioxide is a byproduct of respiration and can be found in many environments but is typically not harmful at the levels encountered in a home unless there is an extreme build-up due to inadequate ventilation. Chlorine is a highly reactive gas that is used primarily as a disinfectant, and while it can be dangerous in high concentrations, such concentrations are usually encountered in specific industrial or cleaning scenarios