Which electromagnetic wave has the longest wavelength

Under the electromagnetic spectrum, visible light has the lowest frequency among the given option. The spectrum ranges from radio waves having low frequency till gamma rays, having the highest one.

Radio waves , on the other hand, have the lowest energies, longest wavelengths, and lowest frequencies of any type of EM radiation.

There are seven regions in the electromagnetic spectrum which in order of lowest to highest frequency are: Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays .

Radio waves usually have the lowest frequency, while Gamma rays have the highest frequency . And as you can see the trend is opposite for wavelength, as frequency and wavelength are inversely related.