Final answer:
The '50' in 'LD50' refers to the lethal dose of a chemical that is sufficient to kill 50% of the test population, usually lab animals like rats or mice. This measure is critical for determining the acute toxicity of substances and is expressed in dose per body weight, usually mg/kg.
Step-by-step explanation:
The "50" in "LD50" stands for the dose required to kill half the members of a tested population. This term is specifically associated with the measurement of a substance's toxicity. The LD50, which stands for lethal dose, 50%, is a standardized measure used to express and compare the toxicity of various chemicals. It indicates the dose value that would be fatal for 50% of the test animals, usually rodents, when exposed to a particular substance under specified conditions.
A common misconception might be that the LD50 relates to the product cost or the percentage of a population that survives, which is not the case. Instead, the term refers to the specific amount of a chemical, expressed in milligrams of the chemical per kilogram of animal body weight (mg/kg), that leads to the death of 50% of the test subjects in a study.