Which of the following soil orders is least developed?

Entisols are known for being the least developed soil order in the USDA soil taxonomy. These soils typically form in environments that have had little time for soil development processes such as horizonation and mineral weathering to occur. Consequently, Entisols often have minimal profile differentiation and may display simple layer structures that lack significant development of organic or clay horizons.

In contrast, other soil orders like Inceptisols, Mollisols, and Alfisols have undergone more extensive weathering and soil-forming processes. Inceptisols show some horizon development but still remain relatively young. Mollisols are characterized by thick, dark topsoil rich in organic matter and are often associated with grassland ecosystems, indicating a more advanced development. Alfisols have a clay-rich horizon and are typically developed in a humid temperate climate, suggesting they have undergone significant development as well.

Thus, considering the criteria of soil development and profile complexity, Entisols emerge as the least developed of the soil orders listed.