Which of the following chemical organic species is / are insoluble in acid or alkali?

The correct answer is Humin.

Key PointsHumins:

• They are insoluble in alkali (high pH) as well as insoluble in acids (low pH).
• They are insoluble in water at all pH.
• They have high molecular weight and are resistant to decomposition.
• They improve the cation exchange capacity of soil and improve soil fertility.

Humic acids:

• They are a mixture of weak aliphatic and aromatic organic acids.
• They are insoluble in water at low pH.
• They are soluble in water at high pH.
• They form stable clay organic complexes.
• They form salts with inorganic trace minerals.

Fulvic acids:

• They are a mixture of weak aliphatic and aromatic organic acids.
• They are soluble in water at all pH.
• They contain more oxygen content than humic acids.
• They are chemically more reactive.
• Their exchange capacity is double that of humic acids.
• They readily enter the plant through roots, stems and leaves and carry minerals to the plants.

Therefore, the correct answer is humin.