Which of the following bands has the lowest maximum permissible exposure for RF safety?
Why RF exposure limits are tightest where the human body absorbs energy most efficiently. A standing adult is roughly a resonant half-wave antenna somewhere around 30 to 300 MHz, so the FCC maximum permissible exposure bottoms out in that range: 1 mW/cm^2 controlled and 0.2 mW/cm^2 uncontrolled. Of the bands listed, 50 MHz falls inside that most restrictive window, so it has the lowest MPE.
Watch out 440 MHz and 1296 MHz are above the resonance region and their limits rise with frequency, while at 3.5 MHz the body is electrically tiny compared to a wavelength and the permitted exposure is far higher.
The body resonates around 30-300 MHz, so VHF gets the strictest limit. 50 MHz is the risky one here.