Question

Assertion (A): Cations adsorbed on soil colloids determine aggregate formation.
Reason (R): Cations form electropositive links between electronegative soil particles.

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is NOT the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

Divalent cations improve soil aggregation by neutralizing colloid charges.

Answer 1

The Correct Option is A

Step 1: Soil colloids carry negative surface charge, so Assertion (A) about cations determining aggregation needs a charge-based explanation.
Step 2: Adsorbed cations like \( \text{Ca}^{2+} \) bridge two negatively charged particles at once, pulling them together into flocs.
Step 3: This bridging is exactly the mechanism behind aggregate formation, so Reason (R) explains Assertion (A) directly.
Step 4: Correct option, both (A) and (R) are correct and (R) is the correct explanation of (A).