First, recall the spectrum of electromagnetic waves, and we know that in the case of electromagnetic waves the frequency is inversely proportional to wavelength.

Now from the above spectrum, we can say that, the relations of wavelength, 

${\lambda }_{\text{radio\hspace{0.17em}waves}}>{\lambda }_{\text{micro\hspace{0.17em}waves}}>{\lambda }_{\text{visible}}>{\lambda }_{\text{x-rays}}$.