Final answer:
The abiotic factor in an ecosystem from the given choices is soil, since it is a non-living entity that significantly influences the environment and supports life.
Step-by-step explanation:
In an ecosystem, abiotic factors refer to the non-living physical and chemical elements that affect the living organisms within. The available choices to identify an abiotic factor are producers, consumers, herbivores, and soil. Among these, soil is the correct choice as it is not alive and provides a substrate where plants can anchor and obtain nutrients, as well as water, which is critical for all life forms.
In contrast, producers, consumers, and herbivores are all biotic components because they are living organisms that either produce biomass, consume other organisms, or feed on plants, respectively. It contains nutrients, water, and provides physical support for plants' roots. Therefore, the correct answer is d. soil.