**Core Concept:**
Golden hair refers to hyperpigmentation of the scalp and body hair, which is a clinical sign seen in certain poisonings. The question is asking about the specific poison that causes this phenomenon.

**Why the Correct Answer is Right:**
Golden hair is a characteristic feature of arsenic poisoning. Arsenic is a toxic element that interferes with melanin synthesis, leading to the hyperpigmentation of the skin and hair. It acts as a reducing agent and competes with sulfur for binding sites in enzymes, particularly sulfhydryl enzymes involved in melanin synthesis. This misguided competition leads to reduced melanin production and increased synthesis of porphyrins, resulting in the characteristic golden hue.

**Why Each Wrong Option is Incorrect:**
A. Arsenic poisoning (Correct, see above explanation)
B. Mercury poisoning: Mercury does not interfere with melanin synthesis but causes skin discoloration, hyperkeratosis, and glossitis.
C. Lead poisoning: Lead causes peripheral neuropathy, abdominal pain, and encephalopathy, but does not lead to golden hair.
D. Selenium poisoning: Selenium is an essential trace element and not associated with golden hair.

**Clinical Pearl / High-Yield Fact:**
Arsenic poisoning should be considered in the differential diagnosis of hyperpigmentation, particularly in areas with known arsenic contamination. Early detection and treatment can prevent severe complications, including skin lesions, gastrointestinal symptoms, and neurotoxicity.