Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).

Assertion (A) : Waterlogged soil typically displays a grayish color due to reduced oxygen levels.
Reason (R) : Upland soil usually maintains a reddish or brownish hue due to its well-aerated nature.

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:

Gray soil color (gleying) indicates prolonged reduction (poor drainage), whereas bright red or orange colors indicate good aeration and oxidation.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Soil coloration is highly influenced by the oxidation state of iron and manganese minerals, which is determined by the soil's aeration status.

Step 2: Detailed Explanation:
Assertion (A) is correct because waterlogging fills soil pores with water, depleting oxygen.
Under these anaerobic conditions, iron-reducing bacteria convert insoluble ferric iron (\(\text{Fe}^{3+}\)) into soluble, mobile ferrous iron (\(\text{Fe}^{2+}\)).
This reduction process leads to "gleying," giving the soil a grayish or bluish-gray color.
Reason (R) is correct because well-drained, well-aerated upland soils contain oxygen that keeps iron oxidized in the ferric state (\(\text{Fe}^{3+}\)), which forms mineral compounds like hematite or goethite that impart red or brown colors.
While both statements are accurate descriptions of soil colors under different aeration regimes, the red color of upland soils (R) does not explain the biological/chemical cause of the grayish color in waterlogged soils (A).

Step 3: Final Answer:
Therefore, both (A) and (R) are correct, but (R) is NOT the correct explanation of (A).