**Core Concept**
Sodium nitroprusside is a potent vasodilator used in the management of severe hypertension and heart failure. It contains a cyanide group, which can be released in the body, leading to cyanide poisoning.

**Why the Correct Answer is Right**
Sodium nitroprusside works by releasing nitric oxide, a vasodilator that relaxes smooth muscle and reduces blood pressure. However, the cyanide group in sodium nitroprusside can be released and bound to cytochrome c oxidase in the mitochondria, inhibiting cellular respiration and leading to tissue hypoxia. This can result in cyanide poisoning, characterized by symptoms such as headache, dizziness, confusion, and even death.

**Why Each Wrong Option is Incorrect**
**Option A:** Nitroglycerin is another vasodilator used to manage angina and hypertension, but it does not contain a cyanide group and is not associated with cyanide poisoning.
**Option B:** Furosemide is a loop diuretic used to treat edema and hypertension, but it is not a vasodilator and does not contain a cyanide group.
**Option C:** Hydralazine is a vasodilator used to treat hypertension, but it does not contain a cyanide group and is not associated with cyanide poisoning.

**Clinical Pearl / High-Yield Fact**
Sodium nitroprusside is a highly effective vasodilator, but its use should be monitored closely due to the risk of cyanide poisoning. This risk can be mitigated by administering sodium thiosulfate, which helps to convert cyanide to thiocyanate, a less toxic compound.

**Correct Answer:** C. Sodium nitroprusside.