which has the longest wavelength and, therefore, the lowest frequency/energy\nradio waves\nvisible…

Brief Explanations:

In the electromagnetic spectrum, radio waves have the longest wavelength, and according to the relationship $c = \lambda\nu$ (where $c$ is the speed of light, $\lambda$ is wavelength, and $\nu$ is frequency), longer wavelength means lower frequency. Also, energy $E = h\nu$ (where $h$ is Planck's constant), so lower frequency implies lower energy.

Answer:

Radio Waves