Final answer:
The soil type that retains water well, feels smooth, and has tiny particles is clay soil. Its fine textured particles explain its ability to hold onto water more effectively than sandy or silt soils.
Step-by-step explanation:
The students are observing characteristics of soil that retains most of the water when tested and feels smooth when rubbed between fingers, with particles that can only be seen with a hand lens. Given these properties, the soil sample in question is most likely clay soil. Clay soil has very small particles that can hold water tightly due to the small size of the pores present, as opposed to sandy soil which has larger pores and cannot retain water as effectively.
As soils vary in texture and particle size, clay soils are able to retain water because the fine particles leave little room for water to escape easily. This is different from sandy soil, which dries out quickly since it has less total water storage between its field capacity and the permanent wilting point. Loam soils, which are preferable for agriculture, are a balanced mixture of sand, silt, and clay, providing both good water retention and drainage.