**Core Concept**
The halo effect in an X-Ray refers to the appearance of a radiolucent ring or halo around a radiopaque object, typically a bone or joint. This phenomenon is caused by the presence of a gas-filled structure, such as an air-filled joint space or a gas bubble in a soft tissue, which creates a contrast effect with the surrounding denser structures.

**Why the Correct Answer is Right**
The halo effect is seen in conditions where there is an accumulation of air or gas in a joint space, such as in osteoarthritis, rheumatoid arthritis, or after a joint injury. This is because the air-filled joint space is less dense than the surrounding bone and soft tissues, creating a radiolucent ring around the joint on an X-Ray. In conditions like osteoarthritis, the joint space narrowing and the presence of subchondral bone sclerosis can also contribute to the halo effect.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not provide a specific condition associated with the halo effect in X-Rays.
**Option B:** This option is incorrect because it is not a valid medical condition that would cause the halo effect.
**Option C:** This option is incorrect because it is not a correct description of the halo effect in X-Rays.

**Clinical Pearl / High-Yield Fact**
The halo effect in X-Rays is a valuable diagnostic clue for conditions involving joint space narrowing and air accumulation, such as osteoarthritis. It is essential to consider the clinical context and correlate the radiographic findings with the patient's symptoms and medical history.

**Correct Answer: C. Gout.**