The major cause of ozone layer degradation is the release of certain chemicals into the atmosphere, which lead to the breakdown of ozone molecules. Among the options given, the compound primarily responsible for this degradation is Chlorofluorocarbons (CFCs).

1. What are CFCs?
   • CFCs are chemical compounds that contain carbon, chlorine, and fluorine.
   • They are used in various applications such as refrigerants, aerosol propellants, and foam-blowing agents.
2. The Effect of CFCs on the Ozone Layer:
   • When CFCs are released into the atmosphere, they eventually make their way to the stratosphere.
   • There, they are broken down by ultraviolet (UV) radiation, releasing chlorine atoms.
   • These chlorine atoms react with ozone (O₃) molecules, causing the ozone to break down into oxygen molecules (O₂).
   • This reaction significantly reduces the amount of ozone in the stratosphere, leading to what is known as the "ozone hole."
3. Why Other Options are Incorrect:
   • CO₂: Carbon dioxide contributes to the greenhouse effect and global warming but does not directly affect the ozone layer.
   • O₂: Oxygen is a fundamental component of the ozone itself and does not contribute to its depletion.
   • CO₃: Carbon trioxide is not a common atmospheric compound and plays no significant role in ozone degradation.

Therefore, the correct answer is CFCs, as they are the primary contributors to ozone layer depletion by releasing chlorine atoms that break down ozone molecules.