Question

K fixing power of clay minerals follows the order:
(A) Illite
(B) Montmorillonite
(C) Kaolinite
(D) Vermiculite

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

Hint:

K fixation depends on the layer charge and interlayer spaces in clay minerals.

Answer 1

The Correct Option is B

The potassium (K) fixing capacity decreases in the following order: Vermiculite $>$ Illite $>$ Montmorillonite $>$ Kaolinite.

Answer 2

Structure-based reasoning: Potassium fixation depends on how tightly a clay mineral's layers can trap K\(^{+}\) ions between them.
Vermiculite has a high layer charge and interlayer spacing just right to wedge K\(^{+}\) ions in place, giving it the strongest fixing power. Illite already contains substantial fixed, non-exchangeable K in its structure, giving it the next-highest fixing capacity. Montmorillonite has expanding 2:1 layers but a lower charge density than vermiculite or illite, so it fixes K only moderately. Kaolinite, being a non-expanding 1:1 mineral with almost no interlayer space, fixes essentially no K.
Ranking by this structural logic reproduces the order Vermiculite \(>\) Illite \(>\) Montmorillonite \(>\) Kaolinite, i.e., (D), (A), (B), (C).