Question

In terms of chemical composition, arrange the elements found in red and yellow soils in descending order of their percentage-

• [(J)] Iron

• [(K)] Magnesium

• [(L)] Insoluble elements

• [(M)] Aluminium
Choose the correct option-

• A. $ \text{K} \rightarrow \text{L} \rightarrow \text{M} \rightarrow \text{J} $
• B. $ \text{L} \rightarrow \text{J} \rightarrow \text{M} \rightarrow \text{K} $
• C. $ \text{J} \rightarrow \text{K} \rightarrow \text{M} \rightarrow \text{L} $
• D. $ \text{M} \rightarrow \text{J} \rightarrow \text{L} \rightarrow \text{K} $

Hint:

In red and yellow soils, remember the simple trend: Silica (insoluble) dominates first, iron gives color, aluminium is moderate, and magnesium is minimal due to heavy leaching.

Answer 1

The Correct Option is B

Concept: Red and yellow soils are highly weathered soils formed mainly in tropical and subtropical regions under conditions of high temperature and moderate rainfall. These soils are characterized by intense leaching, which removes soluble bases and leaves behind a residue dominated by insoluble materials such as silica and quartz. The reddish or yellowish color is mainly due to the presence of iron oxides in different hydration states. Because of long-term weathering, the proportion of nutrients like magnesium is very low, while insoluble minerals remain the dominant fraction.

Step 1: Understanding the general composition of red and yellow soils In highly weathered soils like red and yellow soils, the composition typically follows a consistent trend:

• The largest component is

insoluble material (mainly silica and quartz residues).

• Next comes

iron oxides, which give the characteristic red/yellow coloration.

• Aluminium compounds are present in smaller amounts as part of clay minerals.

• Magnesium and other basic nutrients exist only in trace amounts due to leaching.

Step 2: Interpreting each component

• (L) Insoluble elements: These include quartz and siliceous residues which resist chemical weathering. Since leaching removes most soluble components, these remain in highest proportion.

• (J) Iron: Present mainly as ferric oxide ($\text{Fe}_2\text{O}_3$), responsible for red/yellow coloration, but still much less than insoluble fraction.

• (M) Aluminium: Occurs as alumina in clay minerals, typically less abundant than iron compounds.

• (K) Magnesium: Highly leached basic nutrient, present only in very small trace amounts.

Step 3: Logical ordering based on weathering and leaching Since intense leaching removes mobile ions first and leaves resistant materials behind, the descending order must follow: \[ \text{Insoluble residues} > \text{Iron oxides} > \text{Aluminium compounds} > \text{Magnesium} \] Substituting symbols: \[ \text{L} > \text{J} > \text{M} > \text{K} \] Thus, the correct sequence is: \[ \text{L} \rightarrow \text{J} \rightarrow \text{M} \rightarrow \text{K} \]