Concept:The chemical composition of soil depends mainly on the source material from which the soil is formed.
Explanation:Parent material is the original rock or sediment that breaks down to form soil.
It provides the basic mineral elements, such as calcium, potassium, magnesium, and phosphorus, through weathering.
These minerals directly decide the chemical nature of the soil.
Soil pH and structure are results of the chemical composition, not the main factors that control it.
Living organisms help in adding organic matter and cycling nutrients, but they do not primarily determine the chemical composition.
Thus, among the given options, parent material is the factor that most strongly influences the chemical composition of soil.
Answer:C. parent material