The dose of a substance that kills 50% of a test population.

• A. Lethal dose 50
• B. Median lethal dose
• C. 50% lethal dose
• D. LD-50

Answer: (D)

The main idea here is the dose that is expected to kill half of a test population under specific conditions. This measure is called LD-50, the standard toxicology term, and it’s usually expressed as milligrams of substance per kilogram of body weight (mg/kg). It comes from a dose–response curve and lets scientists compare how toxic different substances are, as well as assess hazards. While the other phrasings describe the same concept in plain language, the conventional and widely used term is LD-50, which is why that option is the best choice. Keep in mind that the exact LD-50 depends on factors like species, route of exposure, age, and health, so it’s a comparative, context-specific metric rather than an absolute universal value.