Question

Humic substances are composed of
(A). Phenols
(B). Quinones
(C). Carboxylic acid
(D). Fatty acid

Choose the correct answer from the options given below:

• A. (A), (B) and (D) only.
• B. (A), (B) and (C) only.
• C. (A), (B), (C) and (D).
• D. (B), (C) and (D) only.

Hint:

Carboxyl (\(\text{-COOH}\)) and phenolic hydroxyl (\(\text{-OH}\)) groups are the main functional groups that give humic substances their high cation exchange capacity (CEC).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Humic substances (humic acid, fulvic acid, and humin) are complex, dark-colored organic compounds that form during the biological decomposition of organic matter in soil.

Step 2: Detailed Explanation:
Humic molecules are complex, high-molecular-weight polymers composed of aromatic ring structures linked together.
Their chemical frameworks contain several key functional groups:
- Phenols (A): Aromatic rings linked with hydroxyl (\(\text{-OH}\)) groups.
- Quinones (B): Cyclic unsaturated diketones that participate in soil oxidation-reduction reactions.
- Carboxylic acids (C): Carboxyl (\(\text{-COOH}\)) groups that supply hydrogen ions, contributing to soil acidity and cation exchange capacity.
Fatty acids (D) are simple aliphatic lipids and are not primary structural constituents of humic polymer networks.
Thus, humic substances are primarily composed of phenols, quinones, and carboxylic acids.

Step 3: Final Answer:
Hence, the correct option is (B), containing (A), (B), and (C).