Explanation: The U.S. Health Department, through agencies like the FCC, establishes Maximum Permissible Exposure (MPE) limits for electromagnetic radiation to ensure public safety. For microwave frequencies (generally above 300 MHz), a widely adopted MPE limit for power density in uncontrolled environments (where general public exposure might occur) is 5.0 mW/cm² (milliwatts per square centimeter). This limit represents the maximum average power density that is considered safe for continuous exposure without adverse health effects. Options A, C, and D represent significantly lower power density values and do not reflect the established MPE limit for microwave energy in an uncontrolled environment as defined by these regulations. These limits are crucial for the safe design and operation of RF-emitting devices, including amateur radio equipment.