Which type of radiation designates a part of the electromagnetic spectrum with frequencies approximately from 300 GHz to 3 kHz, or equivalent, wavelengths approximately from 1 mm to 100km?

Radio waves

The correct answer is option 3. Radio waves.

Radio waves are a type of electromagnetic radiation with wavelengths longer than infrared radiation. They have frequencies ranging from 3 kHz to 300 GHz, corresponding to wavelengths ranging from about 1 millimeter (mm) to 100 kilometers (km).

These waves are used for various purposes, including communication, broadcasting, radar, and remote sensing. Radio waves are commonly used in radio and television broadcasting, wireless communication systems (such as Wi-Fi and cellular networks), and navigation systems (like GPS).

In addition to communication and broadcasting, radio waves are also used in scientific research, such as radio astronomy, where telescopes detect and analyze radio emissions from celestial objects. Overall, radio waves play a crucial role in modern technology and communication systems, enabling wireless communication over long distances.