What is the correct definition of LC50?

The definition of LC50 stands for "Lethal Concentration 50," which is a standard measure used in toxicology to indicate the concentration of a substance, such as a pesticide, that is lethal to 50% of a test population, typically laboratory animals. This metric is crucial for assessing the acute toxicity of chemicals in various environmental media, including air, water, and soil. It provides valuable information for regulatory agencies and researchers about the potential risks of exposure to these substances.

In the context of the given choices, the correct definition emphasizes the relationship between a concentration of a pesticide in the air and its lethality, directly linking to the concept of LC50 as it pertains to the concentration of a toxic substance necessary to harm living organisms. Understanding LC50 values helps in evaluating the safety and environmental impact of chemical agents, especially in relation to the airborne concentration harmful to organisms.