Which substance is inhaled into the lungs along with radon?

Radon decay products (RDPs) are the correct answer because when radon gas is inhaled, it doesn't enter the lungs alone. Radon itself is a radioactive noble gas that can easily move through the soil and into homes. However, as radon decays, it transforms into a series of short-lived radioactive particles called radon decay products. These particles can become attached to dust and other particulates in the air, which can then be inhaled along with the radon gas.

Once inhaled, RDPs can deposit in the lung tissue, increasing the risk of lung cancer over prolonged exposure. It is the inhalation of these decay products that poses a health risk, rather than just inhaling radon gas alone. The other substances listed, such as carbon dioxide, ozone, and nitrogen, do not have the same association with radon and do not represent a secondary inhalation risk linked to radon exposure.