Which of the following soil types has the smallest grains?

Clay is the correct answer because it is characterized by the smallest particle size among the soil types listed. Clay particles are less than 0.002 millimeters in diameter, making them much finer than the other soil types. This fine texture allows clay to retain moisture and nutrients effectively, but also makes it prone to compaction, leading to drainage issues in certain conditions.

In contrast, sand has larger particles that range from 0.05 to 2 millimeters, which gives it good drainage properties but limits its ability to retain moisture and nutrients. Silt, with particles between 0.002 and 0.05 millimeters, is finer than sand but still coarser than clay, giving it moderate water retention and fertility. Loam is a balanced mixture of sand, silt, and clay, and while it is highly fertile and good for agriculture, it does not consist solely of the finest particles like clay does. Therefore, among the options, clay is indeed the soil type with the smallest grains.