Which environmental hazard is caused by the natural decay of radioactive substances in the ground?

Radon is a colorless, odorless gas that results from the natural decay of uranium found in soil, rock, and water. It typically seeps into buildings through cracks in floors and walls, construction joints, and gaps around service pipes. Because it is radioactive, exposure to high levels of radon over time is a significant health risk, primarily increasing the risk of lung cancer.

Understanding radon is crucial for real estate professionals, especially in areas where the geological conditions might lead to elevated radon levels. Testing for radon is advisable during property transactions, and there are mitigation strategies available to reduce its concentration in indoor environments.

The other options listed represent different hazards. Asbestos is a fibrous mineral once commonly used in insulation and other building materials, which poses a risk primarily when disturbed and released into the air. Lead is a toxic metal commonly found in older paints and plumbing, particularly a concern in homes built before 1978. Carbon monoxide is a colorless, odorless gas produced by burning fossil fuels and is dangerous when accumulated in enclosed spaces, rather than from geological processes. Understanding the nature of these distinct hazards helps in promoting safer living environments and complying with regulations in the real estate profession.