Final answer:
The speed at which X-rays and all electromagnetic energy travels in a vacuum is 300,000 km/s, corresponding to the speed of light.
Step-by-step explanation:
X-rays, like all forms of electromagnetic radiation, travel at a certain speed through different mediums. In a vacuum, this speed is a constant for all types of electromagnetic waves, and it is known as the speed of light. The speed of light in a vacuum is approximately 300,000 kilometers per second or 3 × 108 meters per second. Therefore, the velocity at which electromagnetic energy such as X-rays travels is 300,000 km/s.
The correct answer to the student's question is (a) 300,000 km/s, which represents the speed at which electromagnetic waves travel through a vacuum.