On heating ozone, its volume

The reaction when ozone is heated is as follows:

${\mathrm{O}}_3\stackrel{\mathrm{\Delta }}{\to }{\mathrm{O}}_2+\left[\mathrm{O}\right]$

 Thus, we have a stable molecule of oxygen and a highly reactive and unstable nascent oxygen molecule. 

Therefore, based on the process, 1 mole of ozone releases 1 mole of oxygen and 1 mole of nascent oxygen. 

Since ozone is only half an oxygen molecule, even if we assume that the volume of ozone is one litre, it only produces 0.5 litres of nascent oxygen. Thus, from a single litre, a total volume of 1.5 litres was created.