**Core Concept**
The question is testing the understanding of anxiety disorders, specifically the concept of intrusive thoughts and ideas that are characteristic of certain psychiatric conditions. The underlying principle being tested is the distinction between different anxiety disorders, including obsessive-compulsive disorder (OCD), generalized anxiety disorder (GAD), and panic disorder.

**Why the Correct Answer is Right**
The correct answer is related to obsessive-compulsive disorder (OCD), a type of anxiety disorder characterized by the presence of intrusive thoughts, ideas, or images (obsessions) that are recurrent, persistent, and cause significant distress or impairment in daily life. These obsessions are often accompanied by compulsions, which are repetitive behaviors or mental acts aimed at reducing the anxiety associated with the obsessions. The pathophysiology of OCD involves abnormalities in the brain's reward, fear, and cognitive control systems, including the orbitofrontal cortex, anterior cingulate cortex, and basal ganglia.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because generalized anxiety disorder (GAD) is characterized by excessive and persistent worry about everyday things, but it does not typically involve intrusive thoughts or ideas.
* **Option B:** This option is incorrect because panic disorder is characterized by recurrent unexpected panic attacks, but it does not typically involve intrusive thoughts or ideas.
* **Option C:** This option is incorrect because it is a vague term that does not correspond to a specific psychiatric condition.

**Clinical Pearl / High-Yield Fact**
A key feature of OCD is the presence of "just right" feelings, which are feelings of completion or satisfaction that occur when a compulsive behavior is performed.

**Correct Answer: D. Obsessive-Compulsive Disorder**