Question

Given below are two statements: Assertion (A): In soils of humid and sub-humid regions, the colloidal complexes are dominated by aluminium, hydrogen and calcium ions. Reason (R): Aluminium, hydrogen and calcium ions encourage dispersion and consequently they help to form aggregates.

• 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:

Calcium generally improves soil aggregation, while sodium causes dispersion.

Answer 1

The Correct Option is C

Concept:
Soil colloids carry charges and adsorb cations. The dominant cations depend on soil climate, leaching and soil reaction.

Step 1: Check Assertion (A).
In humid and sub-humid regions, leaching is high. Basic cations may be removed and acidic cations like hydrogen and aluminium become important on exchange complexes. \[ A \text{ is correct} \]

Step 2: Check Reason (R).
The reason says aluminium, hydrogen and calcium encourage dispersion and help to form aggregates. This statement is not fully correct. Calcium generally promotes flocculation and aggregation, while dispersion is more commonly associated with sodium-dominated soils. \[ R \text{ is not correct} \]

Step 3: Final conclusion.
Assertion is correct, but the reason given is incorrect. \[ \therefore \text{Correct Answer is (C)} \]