Final answer:
Ozone layer depletion is primarily due to human-made chemical reactions, specifically involving substances like CFCs which destroy ozone molecules in the stratosphere. Option B is correct.
Step-by-step explanation:
The depletion of the ozone layer is happening principally because of chemical reactions involving human-made substances, notably chlorofluorocarbons (CFCs). These substances contain chlorine and bromine, which catalytically break down ozone (O3) molecules into oxygen (O2) in the stratosphere. The breakdown of ozone by these chemicals, which are found in refrigerants, aerosol sprays, and other products, is threatening the layer of good ozone that protects the Earth from the sun's harmful ultraviolet radiation.
Natural atmospheric circulation does affect the distribution and concentration of ozone in the atmosphere, but the principal cause of ozone depletion is the human activity that releases ozone-depleting substances into the atmosphere. Both natural and anthropogenic factors can play a role in ozone layer dynamics, but the sharp decline in ozone levels, leading to the creation of the "ozone hole," is mostly due to these man-made chemicals.