Answer: The ozone(O3) is found in both the stratosphere and troposphere. Ozone in the stratosphere stops harmful ultraviolet rays (UV-B) from reaching Earth.
Most of the CFC and HCFC-based refrigerants cause ozone to deplete. One chlorine molecule can destroy up to 100,000 ozone molecules. The depleted ozone molecules in the stratosphere allow more and more ultraviolet (UV-B) rays to reach Earth which can cause skin cancer and cataracts in humans and animals, decrease the life of plants, weakening of the human immune system.
Hence, United Nations Environment Programme (UNEP) Montreal Protocol created an Index known as Ozone Depletion Protocol (ODP). The higher the ODP the more damage it can cause to the ozone layer.
Old refrigerants like R12, R22, R502, etc which had high ODP have been banned and their manufacturing has been stopped.
Some new generation refrigerants which are HFO, HC, and HFC-based have zero ozone depletion potential.
R1234yf, R1234ze, R290, R600A, R314A, R404A, and R410A have zero ODP value and low to medium Global warming potential. (GWP)