Which of the following is NOT part of the electromagnetic spectrum?

The electromagnetic spectrum encompasses all types of electromagnetic radiation, ranging from radio waves with long wavelengths to gamma rays with very short wavelengths. Infrared, X-rays, and microwaves are all key components of this spectrum. Each of these types of radiation has distinct properties and uses, such as infrared radiation being used in remote controls and thermal imaging, X-rays in medical imaging, and microwaves in cooking and communications.

Sound waves, on the other hand, do not belong to the electromagnetic spectrum because they are mechanical waves that require a medium (solid, liquid, or gas) to travel through. Unlike electromagnetic waves, which can propagate through a vacuum, sound waves rely on the vibration of particles in a medium, making them fundamentally different in nature. This distinction confirms that sound waves are not part of the electromagnetic spectrum.