**Core Concept**
The question is testing knowledge of Wilson's disease, a genetic disorder characterized by excessive accumulation of copper in the liver, brain, and other organs. The presence of Kayser-Fleischer (KF) rings and dystonia are key diagnostic features.

**Why the Correct Answer is Right**
Wilson's disease is caused by mutations in the ATP7B gene, leading to impaired copper excretion. Copper accumulates in the liver, causing damage and triggering an inflammatory response. The liver biopsy will show increased copper levels, which can be detected using a specific stain. Rhodanine is a copper-specific stain that binds to copper ions, making it visible under a microscope.

**Why Each Wrong Option is Incorrect**
**Option A:** **Congo Red** is a stain used to detect amyloid deposits, not copper.
**Option B:** **Sudan Black B** is a stain used to detect lipids and lipoproteins, not relevant in this context.
**Option C:** **Perls Prussian Blue** is a stain used to detect iron deposits, not copper.

**Clinical Pearl / High-Yield Fact**
Wilson's disease should be suspected in any patient with unexplained liver dysfunction, neurological symptoms, or Kayser-Fleischer rings, particularly in children and young adults.

**Correct Answer: D. Rhodanine**