Answer:
Step-by-step explanation:
It's radio waves because the higher the frequency, the shorter the wavelength. From crest to crest, the wavelength of a radio wave is the shortest. The longest would be ultraviolet light, then visible light, then microwaves! And since radio waves have the highest frequency out of any of them, it has the shortest, look up photoelectron spectroscopy and you'll see! Hope it helps!