45 years male, blood sample gives purple-brown colour in Ehrich&;s solution, the substance is
**Core Concept**
The question is testing the student's knowledge of the Ehrlich's reagent test, a chemical test used to identify the presence of certain compounds in a blood sample. Ehrlich's reagent is a solution of p-dimethylaminobenzaldehyde (p-DAB) in ethanol, which reacts with the compound to produce a characteristic color change.
**Why the Correct Answer is Right**
The purple-brown color in Ehrlich's solution is due to the reaction of the compound with the p-DAB reagent. This reaction is specific for the presence of phenylalanine, an essential amino acid. The p-DAB reacts with the phenylalanine to form a Schiff base, which is responsible for the purple-brown color. This reaction is a specific test for phenylketonuria (PKU), a genetic disorder that affects the metabolism of phenylalanine.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the Ehrlich's reagent test or the purple-brown color.
* **Option C:** This option is not related to the Ehrlich's reagent test or the specific color change observed.
**Clinical Pearl / High-Yield Fact**
The Ehrlich's reagent test is a classic example of a chemical test used in clinical diagnosis. It is a simple and specific test for phenylketonuria (PKU), a genetic disorder that requires early detection and treatment to prevent neurological damage. The test is often used in newborn screening programs to detect PKU and other metabolic disorders.
**Correct Answer: D. Phenylalanine**