The E.M. wave with shortest wavelength among the following is

If we look at the spectrum of electromagnetic waves then the order of a wavelength is, ${\lambda}_{gamma} < {\lambda}_{X - ray} < {\lambda}_{UVrays} < {\lambda}_{Visible} < {\lambda}_{Infrared} < {\lambda}_{Microwave} < {\lambda}_{Radio}$, so from the above spectrum the wavelength of gamma rays is minimum and then the wavelength of a radio wave is maximum, so the shortest wavelength is for gamma-rays.