Final answer:
An EM wave with a wavelength of 10³ km is categorized as a radio wave, which is at the end of the electromagnetic spectrum with the longest wavelength and lowest frequency.
Step-by-step explanation:
In the electromagnetic spectrum, an EM wave that has a wavelength of 10³ km falls into the category of radio waves. Among the various types of electromagnetic radiation, radio waves have the longest wavelengths and the lowest frequencies. This spectrum includes, in order of increasing frequency, radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays. A wavelength of 10³ km, which equals 1,000,000 meters, is characteristic of the radio waves used, for instance, in communication technologies like broadcast radio and television.
Given this understanding, when asked what type of EM wave would have a wavelength of 10³ km, we can confidently answer that it would be (1) Radio waves. This part of the spectrum is used for communication over long distances, such as international broadcasting and other forms of wireless communication.