Question

Which type of soil can retain the greatest amount of water- high porosity, low porosity, low permeability or high permeability

Answer 1

The answer is: HIGH POROSITY.
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(although low permeability can be associated with greater water retention. Permeability can be affected by particular size.  For instance, larger particular have larger poles, so fluid (water) can pass through water quickly (higher permeability and less water retention).  As such, smaller particles have smaller pores, so fluid (water) can pass through water LESS quickly (lower permeability and RETAINING MORE WATER.).
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However, "high porosity" is the best choice.