Approximately what fraction of homes nationwide have radon levels at or above 4 pCi/l?

The choice indicating that approximately 1 in 15 homes nationwide have radon levels at or above 4 pCi/l is accurate based on comprehensive studies and data compiled by health organizations, including the Environmental Protection Agency (EPA). This statistic highlights a significant public health concern, as radon is a leading cause of lung cancer among non-smokers.

The rationale behind this figure is grounded in extensive surveys and measurements conducted across various geographic regions in the United States. The value of 4 pCi/l is recognized as a threshold above which radon mitigation is typically recommended. This measure serves as an important guideline for both homeowners and radon measurement professionals when assessing indoor air quality and guiding necessary actions.

While other options suggest much lower frequencies, they underestimate the prevalence of elevated radon levels in homes. The 1 in 15 figure emphasizes the need for awareness and testing, given the potential health risks associated with long-term exposure to radon. Thus, the correct answer reflects both statistical data and a practical understanding of radon exposure risks that affect a notable portion of residences nationwide.