On exposure to air, urine colour changes to olive green in poisoning with: (PGI June 2008)
**Core Concept**
The question is testing the knowledge of a specific chemical reaction that occurs in urine upon exposure to air in the context of a particular poisoning. This reaction is related to the presence of a specific compound in the urine that reacts with oxygen in the air to produce a distinct color change.
**Why the Correct Answer is Right**
The correct answer is related to the presence of para-aminophenol (PAP) in the urine, which is a metabolite of acetaminophen (paracetamol). When PAP is exposed to air, it oxidizes to form a compound that gives urine an olive green color. This reaction occurs due to the enzymatic breakdown of acetaminophen by cytochrome P450 in the liver, resulting in the formation of N-acetyl-p-benzoquinone imine (NAPQI), which is then conjugated with glucuronic acid to form PAP. The presence of PAP in the urine is a classic sign of acetaminophen poisoning.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not relate to the specific chemical reaction that occurs in urine upon exposure to air in the context of acetaminophen poisoning.
* **Option B:** This option is incorrect because it does not accurately describe the chemical reaction that occurs in urine upon exposure to air in the context of acetaminophen poisoning.
* **Option D:** This option is incorrect because it is not related to the specific chemical reaction that occurs in urine upon exposure to air in the context of acetaminophen poisoning.
**Clinical Pearl / High-Yield Fact**
The presence of olive green urine upon exposure to air is a classic sign of acetaminophen poisoning, and it is essential for clinicians to recognize this sign to diagnose and treat the condition promptly.
**Correct Answer:** C. Acetaminophen