Florence test done on dry seminal stain shows dark-brown crystals due to: September 2012, March 2013 (e)
**Core Concept**
The Florence test is a chemical test used to identify the presence of semen in a sample, typically in cases of suspected sexual assault. This test relies on the presence of choline, an enzyme found in semen, which reacts with iodine to produce a characteristic dark-brown crystal precipitate.
**Why the Correct Answer is Right**
The Florence test specifically detects the presence of choline in semen, which is then converted to choline iodide. This compound reacts with iodine to form a dark-brown crystal precipitate, indicating a positive result. The test is highly specific for semen and is often used in forensic analysis.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the Florence test does not detect the presence of other bodily fluids, such as saliva or sweat, which may also contain choline, but in much lower concentrations.
**Option B:** This option is incorrect because the Florence test is not a test for pH levels, which can be variable in different bodily fluids.
**Option C:** This option is incorrect because the Florence test is not a test for the presence of blood, which has a different set of chemical markers.
**Clinical Pearl / High-Yield Fact**
The Florence test is a highly specific and sensitive test for the detection of semen, but it requires a dry seminal stain to produce a positive result. This is because the test relies on the presence of choline, which is more readily available in a dry sample.
**Correct Answer: C. Choline**