Q. Consider the following statements:
Statement I:
In the context of effect of water on rocks, chalk is known as a very permeable rock, whereas clay is known as quite an impermeable or least permeable rock.
Statement II:
Chalk is porous and hence can absorb water.
Statement III:
Clay is not at all porous.
Which one of the following is correct in respect of the above statements?
(a) Both Statement II and Statement III are correct and both of them explain Statement I
(b) Both Statement II and Statement III are correct but only one of them explains Statement I
(c) Only one of the Statements II and III is correct and that explains Statement I
(d) Neither Statement II nor Statement III is correct
UPSC Prelims Question Paper 2025 Download Pdf
Answer & Explanation:
✅Correct Answer: (c) Only one of the Statements II and III is correct and that explains Statement I
Explanation:
Statement I – Correct
Chalk is considered a highly permeable rock because it allows water to pass through it easily. Clay, on the other hand, is regarded as impermeable or least permeable because it severely restricts the movement of water. This contrast is important in understanding groundwater movement and weathering processes.
Statement II – Correct
Chalk is made up of microscopic shells of marine organisms and has a porous structure with interconnected pore spaces. Because of this porosity and connectivity, chalk can absorb and transmit water, which directly explains its high permeability. Hence, Statement II correctly explains Statement I.
Statement III – Incorrect
Clay is not completely non-porous. It does have pores, but these pores are extremely small and poorly connected. Due to this, water movement through clay is very slow, making it low in permeability, but not entirely non-porous. Therefore, Statement III is factually incorrect.
Why Other Options Are Incorrect
- Option (a) is incorrect because Statement III is wrong.
- Option (b) is incorrect because both Statements II and III are not correct—only Statement II is correct.
- Option (d) is incorrect because Statement II is clearly correct.