The dose of a chemical that will kill 50% of the population to which it's applied.

• A. LD50
• B. LC50
• C. TD50
• D. ED50

Answer: (A)

LD50, or lethal dose 50%, is the amount of a chemical that will kill 50% of a tested population under specific conditions. It’s usually expressed as milligrams of substance per kilogram of body weight, showing how much exposure is enough to be fatal for half the group. This metric helps compare how toxic different substances are—the smaller the LD50, the more toxic the chemical, since a smaller amount can be lethal to half the population.

Other terms describe different effects: LC50 refers to the concentration in air or water that kills 50% of the population (relevant to inhalation or aquatic exposure); TD50 is the dose that causes toxic (harmful) effects in 50% of the population (not necessarily death); ED50 is the dose that produces a desired therapeutic effect in 50% of the population.