Final answer:
The true statement about the mineral matter component of soil is that it is a source of potassium, calcium, and magnesium, which are macronutrients vital for plant growth.
Step-by-step explanation:
Among the options provided for the question regarding the mineral matter component of soil, the statement that is true is that 'mineral matter is typically an important source of potassium, calcium, and magnesium in soil'. Mineral matter in the soil comprises about 40 to 45 percent of the soil volume, with the rest being organic matter, water, and air, rather than a very small amount compared to these elements. The organic component of soil, known as humus, is crucial for plant life because it contributes to the soil structure and provides essential nutrients and water to plants. However, humus is not the same as mineral matter; it is part of the organic matter component of soil.
Soil composed entirely of mineral matter without organic matter, water, or air would not typically be able to support abundant plant life due to the lack of organic nutrients and the necessary balance of soil components for plant health. Furthermore, mineral matter does not provide significant amounts of carbon and nitrogen, which are primarily derived from organic material and the activity of living organisms in the soil.