What is a characteristic feature of electromagnetic radiation?

Electromagnetic radiation is characterized by its ability to propagate through a vacuum, which is a significant aspect that distinguishes it from other types of waves, such as sound waves, which require a medium to travel. This property allows electromagnetic waves, which include light, radio waves, and X-rays, to travel across the vast emptiness of space without needing any physical substance to carry them.

The other options highlight concepts that do not apply to electromagnetic radiation in the same way. For instance, electromagnetic waves do not require a medium (as indicated in the first choice), they travel at a constant speed (the speed of light in a vacuum) rather than varying speeds in different media (contrary to the third choice), and they do not primarily convert into kinetic energy upon striking surfaces, as such transformations can be energy-specific and context-dependent.

This fundamental property of being able to traverse a vacuum underlies many phenomena in physics and is essential for understanding wave propagation in various applications, from communications to astronomy.