The correct statement that describes a difference between mechanical waves and electromagnetic waves is:
B. Mechanical waves require a medium to travel through, whereas electromagnetic waves can travel through empty space.
Mechanical waves, such as sound waves and water waves, need a material medium (like air, water, or solid substances) to propagate. In contrast, electromagnetic waves (such as light, radio waves, and X-rays) can move through a vacuum or empty space without the need for a medium.