Geomorphic Processes - 2 - Free MCQ Practice Test with solutions, BPSC

The correct answer is Option C - Macro fauna

Macro fauna are soil animals larger than 2 mm; common examples include earthworms, ants and termites.

These organisms create and maintain burrows and tunnels; their activity produces macropores and increases soil porosity, allowing air to move into and through the soil.

Mesofauna (≈ 0.1-2 mm; e.g., mites, springtails) and microfauna (< 0.1 mm; e.g., protozoa, nematodes, bacteria) mainly assist in fragmentation, aggregation and decomposition of organic matter but do not form the large channels responsible for bulk aeration.

Therefore, the primary agents of soil aeration are macro fauna, so Option C is correct.

The hydration process refers to the chemical reaction that occurs when water interacts with certain materials. Among the options provided, the following points explain why each material is affected differently:

• Granite: This is a hard, igneous rock that is not significantly affected by hydration. It remains stable and does not undergo chemical changes when in contact with water.
• Clay: Clay can absorb water and swell, but this is mainly due to physical changes rather than a true hydration reaction.
• Quartz: Quartz is a mineral that is also resistant to hydration; it does not react chemically with water.
• Salts: Salts undergo hydration when they dissolve in water, leading to changes in their structure and properties.

Thus, the material that is most significantly affected by the hydration process is salts.

Porosity is the percentage of the total volume of rock that is made up of open spaces or pores where water can be stored.

Porosity = (volume of voids / total volume) × 100. Rocks with higher porosity can hold more water.

Permeability is a different property: it is the ability of a rock to allow fluids (like water) to pass through the connected pore spaces.

Because the question asks about the capacity to hold water (storage), the correct term is porosity.

A slump refers to the movement of earth material down a curved or sloping surface due to gravity.
When we say "all Earth materials have a sloping surface," it means that materials like soil, rock, or debris can slowly or suddenly move downslope under the influence of gravity.