LD50 stands for which of the following?

• A. Lethal Dose 50
• B. Lethal Concentration 50
• C. Lethality Dose 50
• D. Lethal Dose Level 50

Answer: (A)

LD50 is the median lethal dose—the amount of a substance required to kill half of the tested population, typically expressed per unit body weight (for example, mg/kg). It reflects acute toxicity and comes from a dose–response relationship, where increasing the dose leads to higher mortality, and the LD50 is the point where 50% die. This term uses dose because it refers to the amount administered to the organism, not the concentration of the substance in the surrounding environment. A related concept is LC50, which uses the lethal concentration in the exposure medium (air, water, etc.) rather than the dose given to the organism. The other phrasings aren’t standard toxicology terms.