Correct Option
The correct option is (a) 2 - 1 - 4 - 3.
Explanation
A soil profile is a vertical section of the soil extending from the surface down to the bedrock. It is composed of distinct layers known as horizons, which differ in texture, colour, depth, and chemical composition. The standard arrangement proceeds from the organic-rich surface layers down to the unweathered bedrock.
Analysis of the Sequence
The correct vertical sequence from the surface downward is as follows:
- 1. Top Soil (Horizon A) [Statement 2]: This is the uppermost layer. It is rich in organic matter (humus) and minerals, providing the necessary nutrients for the growth of plants and vegetation.
- 2. Sub Soil (Horizon B) [Statement 1]: Located immediately below the topsoil, this layer is a transition zone. It contains sand, silt, and clay leached from the layer above but has significantly less organic matter than the topsoil.
- 3. Weathered Rock Material (Horizon C) [Statement 4]: This layer lies below the subsoil. It consists of loose parent material or weathered rock fragments. It represents the first stage in the soil formation process from the underlying bedrock.
- 4. Parent Rock (Horizon R) [Statement 3]: This is the bottommost layer, consisting of unweathered, solid bedrock. It serves as the foundation upon which the soil profile develops.
Therefore, the correct order is 2 (Top Soil) → 1 (Sub Soil) → 4 (Weathered Rock) → 3 (Parent Rock).
Key Takeaway
The standard vertical structure of a soil profile consists of three main layers above the bedrock: Horizon A (Topsoil/Humus), Horizon B (Subsoil/Transition), and Horizon C (Weathered Parent Material), resting on Horizon R (Unweathered Bedrock).