Which of the following is necessary for a system to effectively mitigate radon?

To effectively mitigate radon in a building, the use of an active ventilation mechanism is essential. An active ventilation system helps to continuously exchange indoor air with outdoor air, reducing the concentration of radon gas that can accumulate indoors. This mechanism can include fans or other methods to facilitate air movement, ensuring that any radon-laden air is promptly removed and replaced with fresh air from outside.

In contrast, relying solely on passive air flows might not be sufficient. While passive systems can help manage radon levels, they typically do not provide the same level of control or efficiency as active systems. Placement near exterior walls or the installation of carbon filters may not address the core issue of radon entry into the home and could be more situational or less effective in consistently maintaining low radon levels. Therefore, an active ventilation mechanism is central to providing a reliable and effective radon mitigation strategy.