Which type of wave requires a medium for propagation?

Mechanical waves require a medium for propagation because they are disturbances that travel through a material substance, such as a solid, liquid, or gas. The energy of a mechanical wave travels by displacing the particles of the medium through which it moves. For example, sound waves are mechanical waves that travel through air by causing air molecules to vibrate.

In contrast, electromagnetic waves, such as light and radio waves, do not require a medium and can propagate through the vacuum of space. Transverse waves can be mechanical, but they can also be electromagnetic (as seen in light waves). Thus, while some specific types of waves can travel without a medium, mechanical waves specifically need one to transmit energy and information, making them distinct in this context.