**Core Concept:** EDTA (Ethylenediamine Tetra Acetic Acid) is a chelating agent that forms complexes with divalent cations like calcium. It is used in chelation therapy, a process of removing excessive or toxic levels of divalent cations from the body.

**Why the Correct Answer is Right:** EDTA is mainly used for poisoning with lead, arsenic, and mercury, as these elements form stable complexes with EDTA, allowing for their excretion from the body.

**Why Each Wrong Option is Incorrect:**

A. Calcium poisoning is not the primary indication for EDTA therapy, as it is less effective in removing excess calcium.
B. Calcium poisoning is less common compared to lead and arsenic poisoning, making it an unlikely choice for EDTA therapy.
C. EDTA is not primarily used for treating cadmium poisoning, as it is not effective in removing cadmium from the body.
D. EDTA is not typically used for treating zinc poisoning, as it is less effective in removing excess zinc.

**Clinical Pearl:** EDTA therapy is essential in preventing lead-induced neurotoxicity by chelating lead ions, preventing their entry into nerve cells and causing damage.

**Correct Answer:** C. EDTA is used for cadmium poisoning.

While EDTA is primarily used for managing poisoning caused by heavy-metal ions like lead and arsenic, it is also effective in reducing cadmium toxicity. By forming complexes with cadmium ions, EDTA helps eliminate them from the body, preventing cadmium-induced toxicity and its detrimental effects on various organ systems.