The electromagnetic spectrum is organized in order of increasing frequency or decreasing wavelength. Among the options given, we can categorize these types of electromagnetic radiation from the shortest wavelength (highest frequency) to the longest wavelength (lowest frequency) as follows:

• X-ray: These have very short wavelengths and are on the higher frequency end of the spectrum.
• Ultraviolet (UV): UV radiation has shorter wavelengths than visible light but longer than X-rays.
• Infrared: Infrared radiation has longer wavelengths than visible light, sitting just beyond the red part of the visible spectrum.
• Radiowave: Radiowaves have the longest wavelengths in the electromagnetic spectrum and, correspondingly, the lowest frequencies.

Given this arrangement, radiowaves have the maximum wavelength among the options listed, making Option B the correct answer.