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The energy of EM radiation depends on its frequency, and the lowest frequency corresponds to the lowest energy. Radio waves are at the low end of the energy and frequency spectrum.
The so called visible spectrum. (from red [low frequency] to violet [high frequency].
The range of the visible spectrum is 400THz - 789THz.
The lowest frequency is effectively zero and this would be in the extremely low frequency (ELF) band in the sub-radio range of the electromagnetic spectrum.
color
A spectrum goes from red at the low frequency end to violet at the high frequency end.
Gamma rays
9kHz to 300GHz.
If by greatest frequency you mean highest frequency, we know that the upper end of the electromagnetic spectrum has the greatest frequency. This is the home to the gamma rays. They have the highest frequency, shortest wavelength, and the greatest energy.
Electromagnetic spectrum is a diagram that show the range, or spectrum of electromagnetic waves, in order of wavelength, frequency and energy.
In the E-M spectrum, it is called a frequency meter.
In the electromagnetic spectrum Gamma radiation has the highest frequency.