An allotropic form of oxygen containing three atoms in the molecule. It is a bluish gas, very active chemically, and a powerful oxidizing agent. Ozone is formed when oxygen or air is subjected to a silent electric discharge. It occurs in ordinary air in very small amounts only.
An allotrope of oxygen (symbol O₃) having three atoms in the molecule instead of the usual two; it is a blue gas, generated from oxygen by electrical discharge.