## Core Concept
The question tests knowledge of toxicology, specifically the lethal dose of potassium cyanide (KCN), a potent toxin that inhibits cellular respiration by binding to cytochrome c oxidase in mitochondria.

## Why the Correct Answer is Right
The correct answer, , indicates that the fatal dose of KCN is 150-300 mg. KCN is rapidly absorbed and acts quickly, causing cellular asphyxiation. The mechanism of action involves the inhibition of cytochrome c oxidase, disrupting the electron transport chain and preventing cells from using oxygen, leading to rapid death.

## Why Each Wrong Option is Incorrect
* **Option A:** is incorrect because it suggests a much higher dose, which is not consistent with the known toxicology of KCN.
* **Option B:** is incorrect because, although close, it does not accurately represent the commonly cited fatal dose range for KCN.
* **Option D:** is incorrect because it suggests a much lower dose, which, while toxic, does not align with the lethal dose.

## Clinical Pearl / High-Yield Fact
A key point to remember is that KCN poisoning can be treated with **hydroxocobalamin** (vitamin B12a), which binds cyanide to form cyanocobalamin (vitamin B12), and **sodium nitrite** and **sodium thiosulfate**, which help convert hemoglobin to methemoglobin, enhancing its cyanide-binding capacity.

## Correct Answer: . 150-300 mg