**Core Concept:** X-rays are electromagnetic waves that can penetrate different materials based on their density and atomic number. They are used in medical imaging to visualize the internal structures of an organism, such as bones, tissues, and organs. The human body absorbs and deflects X-rays based on their energy, which is related to the frequency of the waves.

**Why the Correct Answer is Right:** X-rays are produced by electromagnetic radiation with high frequency and short wavelength, typically generated by an X-ray machine. When an electric current is passed through a vacuum tube containing a target (usually a cathode), the electrons are accelerated and collide with the target, emitting secondary particles including X-rays.

**Why Each Wrong Option is Incorrect:**

A. Option A ("Radioactive Decay") is incorrect because it refers to the process by which radioactive substances decay and emit radiation, not the production of X-rays in medical imaging.

B. Option B ("Radiolysis") is incorrect because radiolysis is the process by which ionizing radiation (like X-rays) causes chemical reactions in matter, not the production of X-rays.

C. Option C ("Computer Tomography") is incorrect because computer tomography (CT) uses different imaging techniques like X-rays, gamma rays, or ultrasound, but it is not the process of producing X-rays themselves.

D. Option D ("Millikan Oil Drop Experiment") is incorrect because the Millikan Oil Drop Experiment is a historical experiment that demonstrated the charge of an electron, not the production of X-rays.

**Clinical Pearl:** The correct answer, X-rays, is essential in medical imaging due to their ability to penetrate certain materials and produce images of internal structures. This helps diagnose diseases, fractures, and other abnormalities within the body, without the need for invasive procedures.