**Core Concept**
Pink disease, also known as acrodynia, is a rare condition characterized by inflammation of the skin and soft tissues, particularly affecting the hands and feet. It is caused by chronic exposure to mercury, a heavy metal that can accumulate in the body and cause various toxic effects.

**Why the Correct Answer is Right**
The condition occurs due to the absorption of mercury through the skin or mucous membranes, which is then metabolized to its more toxic form, methylmercury. Methylmercury binds to sulfhydryl groups in proteins, leading to cellular damage and inflammation. The symptoms of pink disease include pink discoloration of the hands and feet, swelling, and pain. The condition is often seen in infants and young children who chew on mercury-containing objects, such as broken thermometers.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while lead poisoning can cause a range of systemic symptoms, it is not typically associated with pink disease.
**Option B:** This option is incorrect because arsenic poisoning can cause a range of symptoms, including skin discoloration, but it is not specifically linked to pink disease.
**Option C:** This option is incorrect because while some heavy metals can cause skin lesions, pink disease is a specific condition associated with mercury exposure.

**Clinical Pearl / High-Yield Fact**
Pink disease is often seen in children who have been exposed to broken thermometers or other mercury-containing objects, and it can be prevented by proper disposal of these materials.

**Correct Answer: D. Mercury**