LD50 refers to the amount of a chemical that kills what proportion of test animals?

LD50, or "lethal dose 50," is a toxicological measure used to determine the dosage of a substance that is expected to cause death in 50% of a test population, typically involving animals. This measurement is critical in understanding the potency of a chemical and its potential risk to health.

When assessing the toxicity of a chemical, researchers conduct tests to observe the effects of various doses on a test group. By analyzing the data, they identify the dose at which half of the test subjects die, thus establishing the LD50 value. This information helps inform safety guidelines and effectiveness for pest control applications, ensuring that chemicals can be used responsibly without undue risk to non-target organisms, including humans and pets.

The other choices indicate different proportions of test animals affected, but the essence of LD50 is specifically tied to that intermediate threshold of 50%, which serves as a standard reference in toxicology and risk assessment.