Question

Given below are two statements, one labelled as Assertion (A) and the other labelled as Reason (R).
Assertion (A): Addition of organic matter to a mineral soil leads to improvement in water holding capacity of the soil.
Reason (R): Under tropical conditions, water holding properties and available water range of a mineral soil due to addition of organic matter may not change materially.
In light of the above statements, choose the most appropriate answer from the options given below.

• 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:

Check whether the reason genuinely explains the assertion, or whether it actually describes an exception to it.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
This question tests whether you can tell apart two statements that are both individually true from a statement pair where one actually explains the other.
Assertion (A) is the general textbook rule taught almost everywhere: adding organic matter to a mineral soil raises its water holding capacity (WHC), because organic matter is porous, holds water on its own surfaces, and helps build stable aggregates that create more pore space.

Step 2: Key Formula or Approach:
Water holding capacity and available water range (AWR) depend mainly on soil texture, structure and clay mineralogy, with organic matter acting as a secondary influence that adds extra water retaining surface area and improves aggregation.
In many tropical mineral soils, the clay fraction is dominated by low activity clays and iron and aluminium oxides rather than the highly active clays common in temperate soils, so structure is already controlled strongly by mineralogy.

Step 3: Detailed Explanation:
Field and lab studies from tropical regions have repeatedly found that, at the organic matter levels normally added through crop residues or manure, the measured change in WHC or AWR of these low activity clay soils is small and often not statistically significant, even though the general rule in (A) still holds true in a broad sense across soils worldwide.
So Reason (R) is also a true, documented observation, it is simply describing a special case where the usual improvement in (A) becomes negligible.
Because (R) reports a situation where the effect in (A) fails to show up clearly, (R) cannot be treated as the explanation for why (A) happens, it instead points to an exception or a limiting condition, which is a different logical role.
This rules out option 1 (which needs R to explain A), and also rules out options 3 and 4, since both A and R are factually correct on their own.

Step 4: Final Answer:
Both (A) and (R) are correct statements, but (R) does not explain why (A) is true, it instead describes a tropical scenario where the improvement in (A) may not be noticeable, so option 2 is the right choice.