**Core Concept**
The ninhydrin test is a chemical assay used to detect and quantify amino acids. It is based on the reaction between ninhydrin, a colorimetric reagent, and the amino group of amino acids, resulting in a purple-colored compound.

**Why the Correct Answer is Right**
The ninhydrin test is specifically designed to detect amino acids due to their primary amino group (-NH2), which reacts with ninhydrin to form a purple-colored compound. This reaction is a result of the condensation between the amino group and the carbonyl group of ninhydrin, leading to the formation of a stable, colored compound. The reaction is highly specific to amino acids, making it a useful tool for detecting and quantifying these molecules.

**Why Each Wrong Option is Incorrect**
**Option A:** The ninhydrin test is not used for detecting bile salts. Bile salts are a type of steroid-based compound that can be detected using other methods, such as the Ehrlich's reagent test.

**Option C:** The ninhydrin test is not used for detecting nucleic acids. Nucleic acids, such as DNA and RNA, can be detected using other methods, such as the diphenylamine test or the orcinol test.

**Option D:** The ninhydrin test is not used for detecting lipids. Lipids are a type of biomolecule that can be detected using other methods, such as the Sudan stain or the Liebermann-Burchard test.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the ninhydrin test is highly specific to amino acids, and any false-positive results can be attributed to the presence of other compounds containing primary amino groups, such as urea or hydrazine.

**Correct Answer:**
✓ Correct Answer: B. Amino acids