Question

Given below are two statements:
Statement (I):The occurrence of two or more patches of colours in soil is called 'mottling'.
Statement (II):The mottled colour is due to residual products of reduction & oxidation of Fe and Mn compounds
In light of the above statements,choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are true.
• B. Both Statement (I) and Statement (II) are false.
• C. Statement (I) is true but Statement (II) is false.
• D. Statement (I) is false but Statement (II) is true.

Hint:

Mottling is a reliable indicator of seasonal water table fluctuation.
Gray colors indicate prolonged reduction, while red/rust spots indicate localized iron oxidation.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Soil color is a key morphological feature that reflects the soil's drainage status, aeration, and mineralogical composition.
Alternating wet and dry cycles lead to characteristic color patterns under fluctuating water tables.

Step 2: Detailed Explanation:
Let us analyze both statements:
- Statement (I): "The occurrence of two or more patches of colors in soil is called 'mottling'."
This is correct.
Mottling refers to the presence of spots or blotches of different colors (typically reds, oranges, yellows, and grays) interspersed within the dominant soil matrix color.
These colored patches are called mottles and indicate seasonal waterlogging.
- Statement (II): "The mottled color is due to residual products of reduction and oxidation of Fe and Mn compounds."
This is also correct.
When soil is saturated (waterlogged), anaerobic conditions develop, causing microbial reduction of insoluble ferric (\(\text{Fe}^{3+}\)) and manganic (\(\text{Mn}^{4+}\)) oxides to soluble ferrous (\(\text{Fe}^{2+}\)) and manganous (\(\text{Mn}^{2+})\) ions.
These soluble ions migrate through the soil solution.
When the soil dries out (oxidizes), these ions precipitate as insoluble oxides and hydroxides in localized zones.
This redistribution results in gray depleted zones (reduced) alongside bright red or orange accumulation zones (oxidized), creating the mottled color pattern.
Therefore, both statements are true.

Step 3: Final Answer:
Both Statement (I) and Statement (II) are true.