There are relatively few substances on earth that are considered toxic or poisonous.

a. True

b. False

The answer would be: b. False

There are many substances that considered toxic. Most of the toxic substance will be determined by LD50, the concentration that will cause a lethal effect in 50% cases. Even excess water could lead to death, but it will need liters of water in short time to do that so it wont be considered toxic. The toxicity is hard to determine because there are variables that cause the substance more dangerous other than concentration