Which among the following when reacted with diazotized sulfanilic acid under alkaline conditions, a red color is formed?
**Core Concept**
The reaction in question is a variant of the diazosulfanilic acid test, which is used to detect the presence of certain compounds, such as nitrites. This test relies on the formation of a red azo compound when the test substance reacts with diazotized sulfanilic acid under alkaline conditions.
**Why the Correct Answer is Right**
The reaction is based on the principle of diazotization, where the diazotized sulfanilic acid reacts with the test substance to form a red azo compound. In the case of nitrites, the diazonium ion from the sulfanilic acid reacts with the nitrite ion to form a red azo compound, which is responsible for the color change. This reaction is facilitated by the alkaline conditions, which help to stabilize the azo compound and promote its formation.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the diazosulfanilic acid test and does not form a red color under alkaline conditions.
* **Option B:** This option may react with diazotized sulfanilic acid, but it does not produce a red color under alkaline conditions.
* **Option D:** This option does not react with diazotized sulfanilic acid under alkaline conditions and therefore does not form a red color.
**Clinical Pearl / High-Yield Fact**
The diazosulfanilic acid test is commonly used to detect the presence of nitrites in urine, which is a marker of urinary tract infection. This test is particularly useful in the diagnosis of conditions such as cystitis and pyelonephritis.
**Correct Answer: C. Hemoglobin.**