Question

Given below are two statements
Statement I: Alkalinity of alkali soil depends upon relative concentration of Na2CO3, NaHCO3 and partial pressure of CO2 in soil solution.
Statement II: Ca2+ and Mg2+ ions increase the flocculation in soil by increasing zeta potential of soil exchange complex.
In light of the above statements, choose the most appropriate answer from the options given below:

• A. Both Statement I and Statement II are correct
• B. Both Statement I and Statement II are incorrect
• C. Statement I is correct but Statement II is incorrect
• D. Statement I is incorrect but Statement II is correct

Hint:

Zeta potential and flocculation:
- Higher zeta potential: Dispersed particles (repulsion).
- Lower zeta potential: Flocculation (attraction).
- Ca2+, Mg2+: Reduce zeta potential, promote flocculation.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
This question tests knowledge of soil chemistry, specifically alkalinity and flocculation.

Step 2: Detailed Explanation:
Statement I:
Alkalinity in alkali soils (sodic soils) is caused by the presence of sodium carbonates and bicarbonates.
The relative concentration of Na2CO3 and NaHCO3 affects soil pH and alkalinity.
The partial pressure of CO2 also influences the equilibrium between carbonates and bicarbonates.
This statement is true.
Statement II:
Ca2+ and Mg2+ ions increase flocculation in soil.
However, they decrease (not increase) the zeta potential.
Zeta potential is the electrical potential at the slipping plane of a colloid.
Flocculation occurs when the zeta potential is reduced, allowing particles to come together.
Divalent cations like Ca2+ and Mg2+ reduce zeta potential and promote flocculation.
The statement says "increasing zeta potential" which is incorrect.
This statement is false.

Step 3: Final Answer:
Thus, Statement I is correct but Statement II is incorrect.
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