37
Agronomy- ICAR JRF/SRF 2024
Multiple Correct
+4
−1
Clay mineral having largest specific surface area is
EXPLANATION
Crop Ecology: Ecological Optima, Environmental Limits, Crop Geography & Agro-Ecological Delineation
- Montmorillonite / Smectite Group Minerals: Possess an expanding 2:1 layer crystal lattice consisting of two silica tetrahedral sheets sandwiching one alumina octahedral sheet.
- Specific Surface Area: Interlayer water and cations expand the interlayer spacing (up to 18 Å), exposing vast internal surfaces in addition to external surfaces, giving smectite/montmorillonite an immense total specific surface area of 600 to 800 $\text{m}^2/\text{g}$. Both Montmorillonite (Option 2) and Smectite (Option 3) represent this mineral group and were recognized as valid answers by NTA. (Correct answer: Options 2 & 3)
- Illite: Non-expanding 2:1 mineral fixed by interlayer potassium ($K^+$); surface area is 80 to 120 $\text{m}^2/\text{g}$.
- Kaolinite: 1:1 non-expanding mineral bonded by strong hydrogen bonds; specific surface area is only 10 to 30 $\text{m}^2/\text{g}$.
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