**Core Concept**
Sanguinarine is a plant-derived alkaloid with toxic properties, particularly affecting the cardiovascular and nervous systems. The sensitivity of various tests is crucial in detecting its presence accurately.

**Why the Correct Answer is Right**
The most sensitive test for sanguinarine is the **Bauer-Kirchner test**, which involves the reaction of sanguinarine with a strong base (sodium hydroxide) and a reducing agent (ferrous sulfate) to produce a reddish-brown color. This reaction is highly specific and sensitive for sanguinarine, allowing for its detection at relatively low concentrations.

**Why Each Wrong Option is Incorrect**
**Option A:** The **Meyer's test** is used for detecting morphine, not sanguinarine. It involves the reaction of morphine with iodine to produce a brown color.
**Option B:** The **Dragendorff's test** is a general reagent for detecting alkaloids, but it is not as sensitive as the Bauer-Kirchner test for sanguinarine.
**Option C:** The **Froehde's test** is used for detecting atropine and related compounds, not sanguinarine.

**Clinical Pearl / High-Yield Fact**
The Bauer-Kirchner test is a highly specific and sensitive test for sanguinarine, but it requires careful handling of strong bases and reducing agents to avoid false positives or contamination.

**Correct Answer:** B. Bauer-Kirchner test