**Core Concept**
Arsenic is a metalloid element with diverse applications in medicine, particularly in the treatment of certain parasitic infections and skin conditions. Its therapeutic effects are often attributed to its ability to interfere with cellular metabolism and DNA synthesis.

**Why the Correct Answer is Right**
Arsenic is used in the treatment of **leishmaniasis**, a disease caused by the protozoan parasite *Leishmania*. The mechanism involves the inhibition of **glycolysis** and the disruption of the parasite's **DNA replication**. Arsenic compounds, such as **arsenic trioxide**, have been shown to be effective in treating visceral and cutaneous leishmaniasis by inducing apoptosis in the parasites.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to arsenic's therapeutic applications.
**Option B:** While arsenic is toxic, it is not used in the treatment of cancer, although some compounds have been investigated for their anticancer properties.
**Option C:** Arsenic is not used in the treatment of tuberculosis.

**Clinical Pearl / High-Yield Fact**
Arsenic trioxide is a potent inhibitor of **topoisomerase II**, an enzyme essential for DNA replication and cell division. This property contributes to its therapeutic effects against Leishmania parasites.

**Correct Answer:** C.