Which soil type has the highest permeability?

• A. Sand
• B. Loam
• C. Clay
• D. Gravel

Answer: (A)

Permeability is determined by how easily water can move through soil, which mainly depends on pore space size and how well those pores are connected. The larger and more connected the pores, the higher the permeability. Gravel has the largest particle size among the options, creating the most open and connected pore network, so water can flow through it the easiest. Sand also allows good flow due to its pores, but not as high as gravel. Loam and clay have smaller pore spaces and stronger capillary forces, which slow or restrict flow. Therefore, gravel has the highest permeability.