One type of wave used to transmit a signal is a ultraviolet wave. infrared wave. radio wave. x-ray wave.

Radio Waves

Explanation:

Radio waves are of longest wavelength and with smallest frequency

So here we can say that the wavelength range is very large and frequency range is less so here these waves are safe to use as these are not dangerous to us.

Since all electromagnetic waves consist of energy of different range depends on the frequency of the waves so in order to use them for communication purpose we have to use those waves which will have less energy so that these waves will remain useful for us.

So here correct answer for communication purpose will be

RADIO WAVE