Which of these frequencies travels at the highest velocity in free space?

Because radio waves are electromagnetic waves, they all travel at the exact same speed in a vacuum (free space) regardless of their frequency or wavelength. That speed is the speed of light, which is approximately 300,000,000 meters per second. A frequent misconception is that higher frequency waves (like microwaves or UHF) must travel faster because they oscillate more rapidly. However, frequency only determines how many cycles occur per second, while the physical forward speed of the wave moving through space remains a universal constant.