Which one of the following waves does not belong to the category of the other three ?

Waves are primarily categorized into mechanical and electromagnetic waves. X-rays, microwaves, and radio waves are all types of electromagnetic waves [2]. These waves consist of linked oscillating electric and magnetic fields and do not require a physical medium to propagate, allowing them to travel through a vacuum [2]. Radio waves have the longest wavelengths, while microwaves are high-frequency electromagnetic waves often used in communication [2]. In contrast, sound waves are mechanical waves [3]. Mechanical waves require a material medium (such as air, water, or solids) to travel because they propagate through the physical compression and rarefaction of matter [3]. Therefore, sound waves do not belong to the same category as the other three, which are all part of the electromagnetic spectrum.

Sources

1. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 20: Earths Atmosphere > Why Are Microwaves And Some Radio Waves Not Reflected By The Ionosphere? > p. 278
2. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 20: Earths Atmosphere > Explanation: > p. 279
3. [3] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 5: Earths Magnetic Field (Geomagnetic Field) > Why Do Sound Waves Travel Faster In A Denser Medium Whereas Light Travels Slower? > p. 64