Final answer:
Different parts of the electromagnetic spectrum are distinguished by their wavelengths or frequencies, with each range corresponding to distinctive properties and uses.
Step-by-step explanation:
What distinguishes different parts of the electromagnetic spectrum is wavelengths (A) or equivalently, their frequencies (B). These characteristics of electromagnetic waves are central in differentiating one type of radiation from another within the spectrum. Electromagnetic waves can range from having very long wavelengths of kilometers (10³ m) to extremely short wavelengths of picometers (10⁻¹² m). Their frequencies correspondingly range from just a few cycles per second to trillions of cycles per second (hertz to gigahertz). Moreover, electromagnetic radiation with different frequencies and wavelengths has distinct properties and uses, thus forming the vast electromagnetic spectrum that includes various types of radiation such as radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.
For example, the visible spectrum, which is only a small part of the electromagnetic spectrum, comprises wavelengths approximately between 400 nm (nanometers) for violet light to 700 nm for red light. As we move from red to violet light within the visible spectrum, the wavelength decreases and the frequency increases, corresponding to an increase in energy.