Explanation

Statement I is correct. Chalk is a soft, sedimentary rock composed primarily of calcium carbonate, with a structure containing large, well-connected pores that allow water to pass through easily — making it a highly permeable rock. Clay, on the other hand, is made up of very fine, tightly packed particles with extremely small pores, through which water moves very slowly — making it one of the least permeable rocks or soils. The contrast between chalk and clay is therefore a classic example of the difference between permeable and impermeable rocks.

Statement II is correct and explains Statement I. Chalk is not only permeable but also highly porous — meaning it contains many tiny holes or voids within its structure that can absorb and retain moisture. This porosity is directly responsible for chalk’s high permeability. Its porous nature also explains why chalk feels damp in humid conditions and crumbles easily when wet. Statement II therefore directly explains why chalk is described as permeable in Statement I.

Statement III is incorrect. Clay is not non-porous — in fact, clay is highly porous and contains many tiny pores between its fine particles. However, these pores are so extremely small that water movement through them is negligibly slow, making clay effectively impermeable. This is why clay retains water and drains slowly despite its high porosity. The statement that clay is “not at all porous” is therefore factually incorrect.

Therefore, only Statement II is correct and it explains Statement I. Statement III is incorrect — clay is porous but impermeable, not non-porous.