The correct answer is A. LD50.
LD50 stands for “lethal dose, 50%”. It is a measure of the toxicity of a substance. It is the dose of a substance that is lethal to 50% of
a population of test animals. LD50 is usually expressed in milligrams of substance per kilogram of body weight.LC50 stands for “lethal concentration, 50%”. It is similar to LD50, but it is the concentration of a substance in the air or water that is lethal to 50% of a population of test animals. LC50 is usually expressed in parts per million (ppm) or milligrams per liter (mg/L).
NOAEL stands for “no observed adverse effect level”. It is the highest dose of a substance that does not cause any adverse effects in a population of test animals. NOAEL is usually expressed in milligrams of substance per kilogram of body weight.
ADI stands for “acceptable daily intake”. It is the daily intake of a substance that is considered to be safe for humans. ADI is usually expressed in milligrams of substance per kilogram of body weight.
In conclusion, the concentration of a material which is lethal to 50% animal is called LD50.