Arrange the following clay minerals with their increasing order of permanent negative charge (moles sites kg−1): (A) Smectite (B) Illite (C) Kaolinite
Choose the correct answer from the options given below:

Correct option is C

1. Explanation of Permanent Negative Charge:
· Clay minerals possess a permanent negative charge due to isomorphous substitution, where higher-valence cations are replaced by lower-valence cations within the clay structure.
· The magnitude of the negative charge depends on the clay mineral's structure and chemical composition.
2. Analysis of the Given Minerals:
· Kaolinite:
· Least negatively charged due to its 1:1 layer structure (one silica tetrahedral sheet and one aluminum octahedral sheet).
· Minimal isomorphous substitution.
· Permanent negative charge: low.
· Illite:
· Intermediate negative charge due to its 2:1 layer structure (two tetrahedral and one octahedral sheet).
· Moderate isomorphous substitution in tetrahedral sheets.
· Permanent negative charge: moderate.
· Smectite:
· Highest negative charge due to significant isomorphous substitution in its 2:1 layer structure.
· It has a large surface area and high cation exchange capacity (CEC).
· Permanent negative charge: high.
3. Order of Increasing Permanent Negative Charge:
· Kaolinite (C) < Illite (B) < Smectite (A).
Thus, the correct answer is (3) (C), (B), (A)
Information Booster: 1. Cation Exchange Capacity (CEC):
· Indicates the ability of clay minerals to hold and exchange cations.
· Order: Smectite > Illite > Kaolinite.
2. Structural Differences in Clays:
· Kaolinite: 1:1 structure; low surface area and minimal negative charge.
· Illite: 2:1 structure with moderate charge and binding strength.
· Smectite: 2:1 structure with high negative charge and swelling capacity.
3. Applications of Clay Minerals:
· Kaolinite: Used in ceramics, paper, and cosmetics due to its low plasticity and low charge.
· Illite: Common in soil fertility studies for its moderate CEC.
· Smectite: Applied in drilling muds, liners for landfills, and water treatment due to its high adsorption capacity.
Additional Knowledge: · Importance of Negative Charge in Clays:
· Influences soil fertility by retaining nutrients like potassium and calcium.
· Affects water retention and soil structure.
· Role in Agriculture:
· Soils rich in smectite are fertile but prone to swelling and shrinkage.
· Kaolinitic soils are less fertile but more stable structurally.