What generally distinguishes Class 2 hazardous materials from the other hazard classes?

Correct answer to question 128 (Hazardous Materials): Class 2 covers gases, including flammable, non-flammable, and poisonous gases

Why

Class 2 covers gases, which are further divided into flammable gases, non-flammable and non-poisonous gases, and poisonous (toxic) gases, each presenting a different type of risk.