Question

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

Assertion (A): Angle of repose of material increases with the increase of moisture content of material.
Reason (R): Increasing moisture content of the material softens the tissue.

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:

Angle of repose is strictly a surface and bulk material handling property.
Always link its variation to surface moisture film tension and surface friction rather than the internal cell-wall properties of the material.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The angle of repose is the steepest angle of descent relative to the horizontal plane to which a granular material can be piled without slumping.
It is heavily influenced by surface properties, shape, and moisture content of the particles.

Step 3: Detailed Explanation:
1.

Assertion (A): When the moisture content of a granular agricultural material (like grain) increases, a thin water film forms around the particles.
This film creates surface tension forces (cohesion) between adjacent particles, which increases inter-particle adhesion.
Consequently, the particles can stack at a steeper angle, increasing the angle of repose. Thus, Assertion (A) is true.
2.

Reason (R): Absorbing moisture indeed softens the internal tissues of organic materials (such as grains). Thus, Reason (R) is true.
However, this internal tissue softening has no physical bearing on the external surface friction and inter-particle cohesion that dictate the pile's stability.
Therefore, while both statements are true, (R) is not the correct physical explanation of (A).

Step 4: Final Answer:
The correct option is 2, which corresponds to both statements being true but (R) is not the correct explanation of (A).