**Core Concept**
Cyanide poisoning is a medical emergency that requires prompt treatment. It occurs when cyanide, a highly toxic substance, is ingested, inhaled, or absorbed through the skin, leading to cellular asphyxiation by inhibiting cytochrome c oxidase in mitochondria.

**Why the Correct Answer is Right**
The treatment of choice for cyanide poisoning is hydroxocobalamin (Cyanokit). Hydroxocobalamin reacts with cyanide to form cyanocobalamin (vitamin B12), which is then excreted in the urine, effectively neutralizing the toxin. This treatment is administered intravenously and is highly effective in reversing cyanide-induced cellular asphyxiation.

**Why Each Wrong Option is Incorrect**
* **Option A:** Naloxone is an opioid antagonist used to reverse opioid overdose, not cyanide poisoning.
* **Option B:** Atropine is an anticholinergic agent used to treat bradycardia and organophosphate poisoning, not cyanide poisoning.
* **Option D:** Sodium thiosulfate is used in the treatment of cyanide poisoning, but it is not the first-line treatment; hydroxocobalamin is preferred due to its rapid onset of action and effectiveness.

**Clinical Pearl / High-Yield Fact**
In cases of suspected cyanide poisoning, activated charcoal may be administered to reduce absorption, but hydroxocobalamin should be given as soon as possible to effectively neutralize the toxin.

**Correct Answer: C. Hydroxocobalamin.