Arrange the following aquifer materials in increasing order of their porosity: (A) Clay (B) Limestone (C) Gravel (D) Fine Sand
Choose the correct answer from the options given below:

Correct option is C

Explanation:
Porosity refers to the percentage of a material’s volume that is void (pore space), which determines its capacity to hold water.
From least to most porous:
· (B) Limestone – Often has very low primary porosity unless extensively fractured.
· (C) Gravel – Has larger pore spaces but less total void volume due to grain size.
· (D) Fine Sand – Smaller grains, tighter packing, hence higher porosity than gravel.
· (A) Clay – Though particles are tightly packed, they have extremely high porosity due to microscopic pores, although permeability is low.
Hence, the correct increasing order of porosity is: Limestone < Gravel < Fine Sand < Clay
Information Booster:
· High porosity ≠ high permeability: Clay has high porosity but low permeability due to very fine pores.
· Aquifer efficiency depends on both porosity and permeability.
· Gravel and sand are commonly used in unconfined aquifers due to better water yield.
Additional Information:
· Option (a) incorrectly starts with clay, which has the highest porosity.
· Option (b) places clay before fine sand, which is incorrect.
· Option (d) ranks gravel before limestone, but limestone typically has lower porosity.