Q.What is Freon-12, what was it used for, and roughly how many ozone molecules can a single chlorine radical from a freon go on to destroy before it is deactivated?

Freon-12, dichlorodifluoromethane ($\text{CCl}_2\text{F}_2$), is the best-known member of the chlorofluorocarbon (CFC) family, adopted widely through the twentieth century as a refrigerant gas in refrigerators/air conditioners and as a propellant in aerosol spray cans, owing to its chemical inertness, low toxicity and convenient liquefaction properties. That same inertness at ground level, however, lets it survive long enough to reach the stratosphere, where UV photolysis releases a chlorine radical that destroys ozone through a catalytic two-step cycle (regenerating the chlorine radical at the end of each cycle rather than consuming it). Because the chlorine is regenerated rather than used up, a single chlorine radical can go on to break down a very large number of ozone molecules -- commonly est …

Connect the 'large number destroyed' fact back to the catalytic (regenerating) nature of the Cl radical cycle -- that is specifically why one …

Treating the large destruction number as if the chlorine were consumed with each ozone molecule destroyed -- the whole point of the catalytic cycle is that the …