Oregon 30-Hour Real Estate Law Practice Test 2025 – Comprehensive All-in-One Guide to Master Your Exam Success!

Radon is a colorless, odorless gas that naturally forms when radioactive materials in the soil, rock, and water decay. It is a significant health concern because prolonged exposure to radon can lead to lung cancer, making it a known carcinogen. This gas can seep into homes and buildings through cracks in floors and walls, construction joints, and other openings. Because of its pervasive nature and the risks associated with it, radon is often a focal point of health and safety regulations related to indoor air quality in residential properties.

The other substances listed do not arise from the decay of rocks and soil. For instance, asbestos is a mineral fiber that can cause health issues when inhaled but originates from different geological processes. Carbon monoxide is a harmful gas produced from burning fossil fuels, and while it's dangerous in enclosed spaces, it is not associated with rock and soil decay. Formaldehyde is a synthetic chemical used in various applications, not a naturally occurring substance related to soil or rock decomposition. Therefore, radon stands out as the correct choice regarding a cancer-causing substance formed through the decay of gases from geological materials.