The amount of inhaled pesticide that kills 50% of a test-animal population is known as what?

• A. Lethal concentration
• B. Label
• C. Larva
• D. Inversion

Answer: (A)

The idea being tested is LC50—the lethal concentration that causes death in 50% of a population exposed by inhalation. It measures acute inhalation toxicity by specifying the concentration of pesticide in the air (or exposure medium) that leads to 50% mortality over a defined exposure period. The smaller the LC50, the more toxic the substance is to organisms when breathed. This is distinct from an LD50, which refers to a lethal dose via other routes. The other options don’t fit because they refer to unrelated concepts: label is product labeling, larva is a developmental stage in insects, and inversion is a weather-related or chemical process not a toxicity metric.