CSIR NET Dec 2015 Q113: Sedimentology

Sand and clay have contrasting physical properties due to their very different particle sizes and pore structures. Sand, having large particles and correspondingly large pore spaces, has low water-holding capacity (water drains through quickly) and high aeration (large pores allow free air/gas exchange); it also has low nutrient-supplying capacity (few reactive surfaces/cation exchange sites for holding nutrients) and, because water passes through it rapidly with minimal surface adsorption, has a poor pollutant-filtering capacity. Clay, with its tiny particles and huge specific surface area, has the opposite properties: high water-holding capacity, low aeration (poor drainage, waterlogging), high nutrient supply capacity (abundant cation exchange sites), and higher pollutant-filtering capacity (adsorbs contaminants onto its large reactive surface area). Given these established relationships, the statement 'water holding capacity of sand > clay' (option 1) is factually incorrect, since clay actually holds substantially more water than sand, making option 1 the identified incorrect statement.

Option 1 is correct as the identified INCORRECT statement: sand's water holding capacity is in fact lower than clay's, not greater, due to sand's large pore spaces that allow water to drain away rather than being retained. Option 2 (aeration in sand > clay) is a true statement, since sand's large pore spaces allow much better air circulation than clay's fine, poorly-connected pores, so it is correctly NOT the answer. Option 3 (nutrient supply capacity of sand < clay) is also a true statement, consistent with clay's much higher cation exchange capacity, so it is correctly not selected. Option 4 (pollutant filtering capacity of sand < clay) is likewise a true statement, since clay's fine particles and large surface area provide much better adsorption/filtration of pollutants than coarse, low-surface-area sand, so it too is correctly not selected as the incorrect statement.