Question

which is not true of electromagnetic waves?
electromagnetic waves travel through vacuums.
electromagnetic waves need a medium to travel.
electromagnetic waves travel faster without mediums.

Explanation:

Electromagnetic waves can travel through a vacuum (like space) without needing a medium. In fact, they travel at the speed of light in a vacuum, which is their fastest speed. Mechanical waves (like sound) need a medium, but electromagnetic waves do not. So the statement that electromagnetic waves need a medium to travel is incorrect.

Answer:

Electromagnetic waves need a medium to travel.