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?

Chalk is a very pure form of limestone, white and rather soft.[1] Karst topography forms in porous water-soluble rocks such as limestone[2], and porous rocks like sandstone have many pore-spaces between grains where water is easily absorbed, and most porous rocks are also permeable.[3] This confirms that chalk is both porous and permeable, making Statement II correct.

Regarding clay, water seeps fastest through gravel, slower through sand, and slowest through clay[4], and clay lowers permeability to water[5]. However, Statement III claiming clay is "not at all porous" is incorrect because argillaceous rocks (clay-based) are mostly impermeable but have very tiny pores[6]. Clay does have some porosity, though minimal.

Therefore, both Statement II and Statement III are factually correct in their essential claims—chalk is porous (Statement II correct) and clay has very low permeability (Statement III essentially correct about impermeability). However, only Statement II properly explains Statement I, as chalk's porosity directly relates to its permeability. Statement III about clay being impermeable is correct but doesn't fully explain why chalk is permeable—it only addresses the clay part of Statement I.

1. [1] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 8: Limestone and Chalk Landforms > Limestone and Chalk > p. 76
2. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 17: Major Landforms and Cycle of Erosion > Conditions for The Formation of Karst Topography > p. 227
3. [3] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 4: Weathering, Mass Movement and Groundwater > Groundwater > p. 42
4. [4] Science-Class VII . NCERT(Revised ed 2025) > Chapter 7: Heat Transfer in Nature > Table 7.5: Seepage of water > p. 100
5. [5] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 25: Agriculture > Soil Components r > p. 366
6. [6] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 13: Types of Rocks & Rock Cycle > Mechanically Formed Sedimentary Rocks > p. 171