**Core Concept**
The question requires identifying a radioprotector, which is a substance that helps protect cells from the harmful effects of ionizing radiation. Radioprotection is a critical concept in radiation oncology and nuclear medicine.

**Why the Correct Answer is Right**
The correct answer is Amifostine, which is a well-known radioprotector that works by scavenging free radicals and protecting DNA from damage. It is a phosphorothioate analogue of cytosine and is used to reduce the severity of xerostomia (dry mouth) and other side effects associated with radiation therapy to the head and neck. Amifostine acts by inhibiting the enzyme glutathione reductase, which is involved in the production of reactive oxygen species that can damage DNA.

**Why Each Wrong Option is Incorrect**
**Option A:** Hydroxyurea is a chemotherapeutic agent that works by inhibiting ribonucleotide reductase, but it is not a radioprotector.
**Option B:** Cisplatin is a chemotherapy drug that works by cross-linking DNA, but it is not a radioprotector.
**Option C:** Metronidazole is an antibiotic that works by inhibiting DNA synthesis, but it is not a radioprotector.

**Clinical Pearl / High-Yield Fact**
Amifostine is the only radioprotector approved by the FDA for use in humans, and it is typically administered as an intravenous infusion before radiation therapy.

**Correct Answer: C. Metronidazole is a wrong option. Amifostine is the correct answer.**