What characteristic defines loose soil?

Loose soil is characterized by its inability to hold together, which is why the answer highlighting that it "does not hold together" is the correct choice. When soil is loose, it typically has larger particles and more space between them, resulting in lower cohesive strength. This means that when disturbed or when pressure is applied, the particles do not cling together effectively, leading to a crumbly or disintegrated structure.

The other options do not accurately reflect the nature of loose soil. For example, soil that holds together well would suggest a denser or more cohesive type of soil, which is the opposite of loose soil. Similarly, minimal pressure is needed to break apart loose soil, not significant pressure, as loose aggregates are already prone to disintegration. High water retention capability is also not a defining characteristic of loose soil; in fact, loose soils often drain faster, resulting in less water retention compared to denser soils that can hold more moisture due to their compactness.