Which of the following is an odorless radioactive gas produced from the decay of other materials?

Radon is an odorless radioactive gas that forms naturally from the decay of uranium, which is found in soil, rock, and even water. During the natural decay process, uranium transforms into radium and eventually into radon gas. Since radon is colorless and tasteless, it cannot be detected without the use of specific testing equipment, making it particularly concerning as a health hazard in homes and buildings, especially in areas with high uranium content in the ground.

In contrast, asbestos is a group of minerals that can cause health risks when inhaled but is not a gas nor radioactive. UFFI (Urea-Formaldehyde Foam Insulation) is an insulation material that can release formaldehyde gas but does not involve radioactivity or decay processes. Lead is a toxic heavy metal that can accumulate in the body and cause significant health issues, yet it is not a gas and is not formed through radioactive decay like radon. Understanding these distinctions highlights why radon is the correct answer in this context.