**Question:** X-rays are produced when -

A. Electrons are accelerated to high speeds and collide with atoms
B. Radioactive atoms emit radiation
C. Positive charges are accelerated and interact with matter
D. Electricity is passed through a gas

**Core Concept:** X-rays are a form of electromagnetic radiation with a higher frequency than visible light, and are produced through interactions between charged particles and matter. They are used in medical imaging to visualize internal structures due to their ability to penetrate certain materials and interact with atomic nuclei.

**Why the Correct Answer is Right:**

X-rays are produced when electrons are accelerated to high speeds and collide with atoms (Option A). In this process, the high-energy electrons collide with the inner shell electrons of an atom, causing them to be ejected. This leaves a vacancy in the inner shell, and the electron from a higher-energy outer shell falls into the vacant inner shell, releasing a burst of high-energy electromagnetic radiation, namely X-rays.

**Why Each Wrong Option is Incorrect:**

Option B (Radioactive atoms emit radiation) is incorrect because it refers to a different type of radiation, specifically gamma rays, which are emitted by unstable atomic nuclei. X-rays are not produced when radioactive atoms emit radiation.

Option C (Positive charges are accelerated and interact with matter) is incorrect because it describes the process of charged particles accelerating and interacting with matter, but does not specifically mention electrons colliding with atoms to produce X-rays.

Option D (Electricity is passed through a gas) is incorrect because it refers to the production of X-rays through the process of fluorescence, which occurs when high-energy photons (like visible light) pass through a gas and excite the electrons in the gas molecules. This process produces visible light, not X-rays. The correct answer (Option A) describes the production of X-rays through electron collisions, which is the actual process in radiography and imaging techniques.

**Clinical Pearl:**

In medical imaging, X-ray machines use electron accelerators to produce X-rays, which are then directed at the patient's body to create detailed images of internal structures. This process helps diagnose and treat various medical conditions, as X-rays can penetrate tissues and interact with atomic nuclei, revealing key anatomical details.