**Core Concept**
The question tests the understanding of **chelation therapy** and the specific use of **Dimercaprol (BAL)** in treating heavy metal poisoning. Dimercaprol is a chelating agent that binds to heavy metals, facilitating their excretion.

**Why the Correct Answer is Right**
Dimercaprol is effective in treating poisoning by **arsenic**, **mercury**, and **lead** due to its ability to form stable complexes with these metals. However, it is not effective for all types of heavy metal poisoning.

**Why Each Wrong Option is Incorrect**
**Option A:** Inadequate information is provided to assess this option.
**Option B:** Similarly, this option cannot be evaluated due to missing details.
**Option C:** Without specifics, the incorrectness of this choice cannot be determined.
**Option D:** Same as above, lacks necessary information for assessment.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that **Dimercaprol** is contraindicated in **iron** and **cadmium** poisoning, as it can worsen the condition. Always consider the specific heavy metal involved when choosing a chelation therapy.

**Correct Answer:** D. Iron poisoning