**Core Concept**
The management of heavy metal poisoning, such as mercury, involves the use of chelating agents that bind to the metal ion, facilitating its excretion from the body. This concept is crucial in emergency medicine and toxicology.

**Why the Correct Answer is Right**
Dimercaprol, commonly known as BAL (British Anti-Lewisite), is a specific chelating agent used to treat heavy metal poisoning, including mercury. It works by forming a stable complex with the metal ion, allowing it to be excreted in the urine. The mechanism involves the reaction of BAL with the mercury ion, resulting in the formation of a mercaptide complex, which is then eliminated from the body. This process is essential in reducing the toxicity of mercury and preventing further damage to the body's tissues.

**Why Each Wrong Option is Incorrect**
**Option A:** Calcium disodium edetate is a chelating agent used to treat lead poisoning, not mercury poisoning. It works by binding to the lead ion, but it is not the correct choice for mercury poisoning.
**Option B:** Desferrioxamine is a chelating agent used to treat iron poisoning, not mercury poisoning. It works by binding to the iron ion, but it is not effective against mercury.
**Option C:** Penicillamine is a chelating agent used to treat copper poisoning and Wilson's disease, not mercury poisoning. It works by binding to the copper ion, but it is not the correct choice for mercury poisoning.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that different heavy metals require specific chelating agents for treatment. The choice of chelating agent depends on the type of metal ion involved and the severity of the poisoning.

**✓ Correct Answer: D. BAL. Dimercaprol (BAL) is a chelating agent used to treat heavy metal poisoning, including mercury.**