## Core Concept
The Xanthoproteic test is a chemical test used to detect the presence of proteins. It involves the reaction of proteins with concentrated nitric acid, resulting in a yellow-colored product.

## Why the Correct Answer is Right
The Xanthoproteic test is specifically used for detecting proteins. When proteins are treated with concentrated nitric acid, the nitration of aromatic rings in amino acids like tyrosine, tryptophan, and phenylalanine occurs, leading to the formation of yellow-colored nitro derivatives. This reaction is the basis for the Xanthoproteic test, making it a useful tool for identifying proteins in a sample.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because the Xanthoproteic test is not primarily used for detecting fats or lipids; other tests like the Sudan III test are used for that purpose.
- **Option B:** This option is incorrect as the Xanthoproteic test does not specifically target carbohydrates; tests like Benedict's test are used for carbohydrate detection.
- **Option C:** This option might seem plausible but is incorrect because, although nucleic acids can be detected through other means, the Xanthoproteic test is specifically for proteins.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the Xanthoproteic test gives a positive result (yellow color) with proteins. This test can be used in clinical settings to quickly assess the presence of protein in urine (for kidney function assessment) or in other biological samples.

**Correct Answer:** C. proteins.