‘Chroma’ variable in determination of soil colour represents

Correct option is D

The correct answer is (D) Relative purity of the colour

Explanation:
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• Soil color is standardized using the Munsell Color System, which defines color based on three variables: Hue, Value, and Chroma.
• Chroma (D): Represents the relative purity, strength, or saturation of the color. A low chroma indicates a dull or grayish color (high neutral content), while a high chroma indicates a bright, vivid color.
• In soil science, low chroma (usually $\le 2$) is often an indicator of poor drainage or waterlogged conditions (gleying).

Information Booster:
• Hue: Represents the dominant spectral color (e.g., 10YR, 5R). It relates to the wavelength of light.
• Value: Represents the relative lightness or darkness of the color. It ranges from 0 (absolute black) to 10 (absolute white). Darker soils (low value) usually contain more organic matter.
• A typical soil color notation looks like: 10YR 3/2 (Hue 10YR, Value 3, Chroma 2).

Additional Knowledge:
• Option A (Spectral region): This is the definition of Hue.
• Option C (Relative brightness): This is the definition of Value.
• Munsell color charts are essential in soil surveys for classifying soil horizons and drainage classes.