When ultraviolet (UV) light strikes ozone (O_3) molecules in the atmosphere, what is the primary effect?

• A. The ozone molecules reflect the UV light without any chemical change.
• B. The ozone molecules absorb the UV light and undergo decomposition into O_2 and O.
• C. The ozone molecules are unaffected by UV light and remain stable.
• D. The ozone molecules emit visible light after absorbing the UV light.

Answer: (B)

Verified step by step guidance

1. Understand the nature of ozone (O_3) in the atmosphere and its interaction with ultraviolet (UV) light. Ozone plays a crucial role in absorbing harmful UV radiation from the sun.
2. Recall that when ozone absorbs UV light, it gains energy that can break chemical bonds within the molecule, leading to a chemical reaction rather than just reflecting or remaining unchanged.
3. Recognize that the absorption of UV light by ozone causes it to decompose into molecular oxygen (O_2) and a single oxygen atom (O). This is a photodissociation process.
4. Note that this decomposition is important because the free oxygen atom (O) can react with other ozone molecules or oxygen molecules, contributing to the ozone-oxygen cycle that protects the Earth from UV radiation.
5. Conclude that the primary effect of UV light striking ozone molecules is absorption followed by chemical decomposition into O_2 and O, rather than reflection, stability, or emission of visible light.