All the following can be used as irritant poisons, but which one of them when taken internally is not fatal?
**Core Concept**
The question tests the knowledge of irritant poisons, which are substances that cause damage to tissues and organs by chemical means. These substances can cause severe local and systemic effects, including burns, ulcers, and respiratory failure.
**Why the Correct Answer is Right**
The correct answer is **D. Cyanide**. Cyanide is a potent toxin that can cause cellular asphyxiation by inhibiting the electron transport chain in mitochondria. However, when taken internally in small quantities, cyanide can be rapidly metabolized and excreted by the body, making it less likely to be fatal compared to other irritant poisons. This is because cyanide has a short half-life and is rapidly converted to thiocyanate, which is then excreted by the kidneys.
**Why Each Wrong Option is Incorrect**
**Option A:** Hydrochloric acid is a strong acid that can cause severe burns and ulcers in the gastrointestinal tract, leading to perforation, peritonitis, and death. It is highly fatal when taken internally.
**Option B:** Sulfuric acid is another strong acid that can cause severe chemical burns and systemic toxicity, leading to respiratory failure, cardiac arrest, and death. It is highly fatal when taken internally.
**Option C:** Phosphorus is a highly toxic substance that can cause severe gastrointestinal and hepatic toxicity, leading to liver failure, renal failure, and death. It is highly fatal when taken internally.
**Clinical Pearl / High-Yield Fact**
Remember that irritant poisons can cause severe local and systemic effects, and their toxicity can vary depending on the dose, duration of exposure, and individual susceptibility. Always consider the mechanism of action and potential systemic effects when assessing the toxicity of a substance.
**Correct Answer:** D. Cyanide is not fatal when taken internally in small quantities because it can be rapidly metabolized and excreted by the body.