LD50 is the dose at which 50% of treated animals die. Which of the following statements is true about LD50?

• A. The dose at which 50% die in treated animals
• B. The dose that produces therapeutic effect in 50% of animals
• C. The dose that causes toxic effect in 50% of humans
• D. The dose that guarantees safety in animals

Answer: (A)

LD50 is defined as the dose that kills 50% of a defined group of animals under specific conditions. This makes it a measure of acute lethality and a way to compare how toxic different substances are. The statement that matches this definition correctly describes the lethal threshold for half the population, which is why it is true. The other ideas mix up concepts: a dose that produces the therapeutic effect in 50% of animals is an ED50, not an LD50; LD50 is not about humans and cannot be directly translated to human safety; and there is no dose that guarantees safety—the LD50 is a statistical estimate that depends on species, route of exposure, and experimental conditions.