Clay Mineralogy MCQ with answer and solution

Concept

Sodium clay has a dispersed structure with very low permeability, so it is used in the impervious core of earth dams.

Step-by-step solution

1. The core of an earth dam must stop seepage of water. 2. So the core material must have very low permeability. 3. Sodium clay (sodium montmorillonite) has a dispersed structure and a thick double layer of water around its particles. 4. This makes its permeability very low. 5. So the answer is (D) low permeability.

Explanation

The core of an earth dam acts as a water barrier. Sodium clay has very fine particles with a dispersed structure, so water passes through it very slowly. Because of this very low permeability, it is a good core material.

Why the other options are wrong

A: High permeability would let water seep through, which is not wanted in a core. B: Sodium clay actually has low strength, so strength is not the reason. C: Clays have high porosity, not low porosity.

Shortcut

Dam core = impervious = low permeability.

Common mistake

Thinking low porosity means low permeability. Clay has high porosity but still very low permeability.