Which of the following statements are true regarding the breakdown of stratospheric ozone? I. It can originate from the emission of chlorofluorocarbons (CFCs). II. It can be initiated by a free chlorine (Cl). III. It prevents UV rays from reaching Earth’s surface.

CFCs can release chlorine atoms in the stratosphere, and free chlorine can react with ozone and help break it down, so I and II are true. Ozone normally absorbs much of the Sun’s UV radiation; its breakdown allows more UV to reach Earth’s surface, so III is false. The correct choice is I and II.

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