Which sequence below is listed from the smallest particle size to the largest particle size: Clay, silt, sand, gravel. Which type of soil is the smallest in particle size: Clay . Which of the following represents the best range of pH for plant growth: Weak acidic and neutral. Which range of pH is best for plant growth: . What is beneficial about topsoil: Suitable for plant growth. Which physical property causes these soils and other materials to layer in this sequence: Density. Which of the following describes a soil horizon: A layer of soil. What is soil: A mixture of weathered rock, organic matter, air, and water. Soil that allows water to pass through it is considered to be _______________: permeable. The decayed organic matter in soil is called _______________: humus