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?
Show answer
Answer: C. Statement I is correct: chalk lets water pass easily (permeable), while clay hardly lets it pass. Statement II is correct and explains this: chalk is porous and absorbs water. Statement III is wrong: clay is actually very porous (it holds a lot of water), but its pores are so tiny and poorly connected that water cannot flow through it. So only Statement II is correct and it explains Statement I.
Watch for: Porosity (how much water a rock holds) is not the same as permeability (how easily water passes through); clay is porous but impermeable.
Why the other options are wrong
- A. Wrong: Statement III is false, because clay is porous.
- B. Wrong: Statement III is false, so both are not correct.
- D. Wrong: Statement II is correct.
Source to check: NCERT Class XI, Fundamentals of Physical Geography (rocks and groundwater); basic geology texts on porosity and permeability.
Answer from the official UPSC key. Written and fact-checked by AI against the official key. Spotted a mistake? Report it.