Arrange the following environmental materials found in the colloidal size fraction in their increasing order of Cation Exchange Capacity (CEC) (c mol(+) kg⁻¹):
A. Kaolinite B. Montmorillonite C. Quartz D. Organic matter
Choose the most appropriate answer from the options given below:

Correct option is C

1. Cation Exchange Capacity (CEC):
· CEC measures the ability of a material to exchange cations with the surrounding environment.
· It is expressed in cmol(+) kg⁻¹ and depends on the surface area and charge density of the material.
2. Material-Specific CEC Values (approximate ranges):
· Quartz: ~0 cmol(+) kg⁻¹ (negligible CEC due to its inert structure).
· Kaolinite: ~3–15 cmol(+) kg⁻¹ (low CEC, due to its simple 1:1 layer structure).
· Montmorillonite: ~80–150 cmol(+) kg⁻¹ (high CEC, due to its 2:1 layer structure and large surface area).
· Organic matter: ~150–250 cmol(+) kg⁻¹ (very high CEC, due to its large number of negatively charged functional groups like carboxylic and phenolic groups).
3. Increasing Order of CEC:
· Quartz < Kaolinite < Montmorillonite < Organic matter
The correct order is C (Quartz) < A (Kaolinite) < B (Montmorillonite) < D (Organic matter).
Information Booster: 1. Importance of CEC in Soil Science:
· Determines nutrient-holding capacity of soils.
· Higher CEC materials retain more essential cations like potassium (K⁺), calcium (Ca²⁺), and magnesium (Mg²⁺).
2. CEC and Soil Fertility:
· Soils with higher organic matter and clay content tend to have higher fertility due to better cation retention.
3. Factors Affecting CEC:
· pH: Higher pH increases CEC due to the deprotonation of functional groups.
· Mineral Type: The structure of clay minerals significantly impacts CEC values.
4. CEC Measurement Units:
· CEC is commonly expressed in cmol(+) kg⁻¹, equivalent to the charge in centimoles of positive ions per kilogram of material.