## Core Concept
Sodium nitrite is used in the treatment of cyanide poisoning. It works by inducing **methemoglobinemia**, a condition characterized by the presence of an abnormal amount of methemoglobin in the blood. Methemoglobin has a higher affinity for cyanide than cytochrome c oxidase, thereby mitigating the toxic effects of cyanide on cellular respiration.

## Why the Correct Answer is Right
The correct mechanism of action of sodium nitrite in cyanide poisoning involves the conversion of hemoglobin to **methemoglobin**. Methemoglobin then binds with cyanide to form **cyanomethemoglobin**, which is a harmless compound. This action effectively sequesters the cyanide ions, preventing them from inhibiting **cytochrome c oxidase** in the mitochondria and thus restoring cellular respiration.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it does not accurately describe the mechanism by which sodium nitrite acts in cyanide poisoning.
- **Option B:** This option is incorrect as it also does not accurately represent the mechanism of action of sodium nitrite.
- **Option D:** This option is incorrect because it too fails to accurately describe how sodium nitrite works in treating cyanide poisoning.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the treatment of cyanide poisoning with sodium nitrite and **sodium thiosulfate** is aimed at converting cyanide into thiocyanate, which is much less toxic. The use of sodium nitrite to induce methemoglobinemia is a critical step in this process. This combination therapy is a classic approach in managing acute cyanide poisoning.

## Correct Answer: B. Converts Hb to Methemoglobin.