Speed of X-ray is equal to:
**Core Concept**
The question tests the understanding of the physical properties of X-rays, specifically their speed. X-rays are a form of electromagnetic radiation, and their speed is a fundamental constant in physics.
**Why the Correct Answer is Right**
The correct answer is based on the fact that X-rays, being electromagnetic waves, travel at the speed of light in a vacuum. This speed is approximately 299,792 kilometers per second (or about 186,282 miles per second).
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not match the known speed of light.
**Option B:** This option is also incorrect as it does not correspond to the speed of X-rays.
**Option C:** Similarly, this option is wrong because it does not represent the speed of electromagnetic radiation like X-rays.
**Clinical Pearl / High-Yield Fact**
It's crucial to remember that the speed of X-rays is the same as the speed of light in a vacuum, which is a fundamental principle in physics and radiology.
**Correct Answer:** Correct Answer: D. Speed of light.