Which phrase describes an electromagnetic wave? a. a transverse wave consisting of changing electric fields and changing magnetic fields b. a longitudinal wave that can travel through matter or empty space c. a transverse wave consisting of electric fields and magnetic fields traveling through matter

 option A. a transverse wave consisting of changing electric fields and changing magnetic fields.

Explanation:

An electromagnetic wave is a wave generated by the vibration of perpendicular electric and magnetic fields, which may progate through vacuum (empty space) or a material medium.

All electromagnetic waves propagate at the same speed in vacuum. This speed is approximately 3.0 × 10⁸ m/s. Which is generally referred as the speed of light, but it is the same constant speed of any electromagnetic wave in the vacuum, c.

In general, waves transfer energy when they travel, but only electromagnetic waves can travel in vacuum. The waves that cannot travel in vacuum are named mechanical waves (they need a medium to travel).

There are two types of waves depending on how they propagate: transverse waves and longitudinal waves. The transverse waves travel perperdiculary to the direcction of the vibration, while longitudinal waves travel parallel to the direction of the vibration.

The classical example of transverse waves is a rope that oscilates up and down. The classical example of  longitudinal waves is a spring that you pull and push by an end and so it  moves forward and back. Sound is also a longitudinal wave.

This is  how you discard the other options:

B. a longitudinal wave that can travel through matter or empty space: no, because, as said, electromagnetic waves are transverse not longitudinal.

C. a transverse wave consisting of electric fields and magnetic fields traveling through matter: no, because a unique characteristic of electromagnetic waves is that they travel through empty sapce.