Gamma rays
I think in the ultraviolet region of the electromagnetic spectrum.
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.
Radio waves have a lower frequency than microwaves in the electromagnetic spectrum. They have the lowest frequency and longest wavelengths of all the electromagnetic waves.
Gamma rays
Frequency determines this.
The radio frequency portion of the electromagnetic spectrum uses radio telescopes.
The answer is electromagnetic spectrum
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.
Electromagnetic spectrum is formed due to the difference of wavelengths and frequency of electromagnetic radiations as they are orderly distributed.
The radio frequency portion of the electromagnetic spectrum uses radio telescopes.
Extremely low frequency (ELF) radio waves. They can have wavelengths of over 60,000 miles (100,000 km) and frequencies from 3 to 300 Hz.
The electromagnetic spectrum organizes different types of electromagnetic waves according to their wavelength or frequency.