Which of the following radiation types has the longest wavelength?

Radio waves have the longest wavelength among the types of radiation listed. In the electromagnetic spectrum, wavelengths are arranged from the shortest to the longest. X-rays have significantly shorter wavelengths than both ultraviolet rays and visible light. Ultraviolet rays, while having a longer wavelength than X-rays, are shorter than visible light. Visible light itself occupies a small portion of the spectrum and is shorter in wavelength than radio waves.

Radio waves can have wavelengths that range from about one millimeter to several kilometers, making them the longest wavelength radiation mentioned in this context. This characteristic allows them to be used for various applications, such as communication and broadcasting, where longer wavelengths can travel distances and penetrate through obstacles more effectively than shorter wavelengths.