Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : Weathering produces minerals which is assigned with a weathering index.
Reason (R) : The sequence of weathering is largely controlled by intensity and capacity factor as a fraction of time.
In light of the above statements, choose the correct answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

Mineral weathering is a dynamic process driven by thermodynamic forces.
The intensity factor determines *how fast* the reaction can occur, while the capacity factor determines *how much* mineral can be weathered over time.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Weathering is the physical disintegration and chemical decomposition of rocks and minerals.
This process converts primary minerals into secondary minerals and soluble ions.
The stability and weathering sequence of minerals are classified using weathering indices, such as Jackson's weathering index.

Step 2: Detailed Explanation:
Assertion (A): Chemical weathering converts unstable primary minerals into more stable secondary minerals.
Scientists assign a weathering index (such as Jackson's 1 to 13 stages) to these minerals based on their relative resistance to weathering. Thus, Assertion (A) is true.
Reason (R): The rate and sequence of mineral weathering are determined by:
- Intensity factor: The chemical driving force of weathering (e.g., temperature, soil solution pH, redox potential).
- Capacity factor: The total volume of weathering agents available (e.g., volume of leaching water).
These factors act over a given period (fraction of time) to determine the mineralogical composition of the soil. Thus, Reason (R) is true.
This thermodynamic and kinetic explanation directly accounts for why different minerals are placed at specific stages of the weathering index.
Therefore, both statements are true, and (R) is the correct explanation of (A).

Step 3: Final Answer:
Both statements are true, and (R) is the correct explanation of (A).