AQA A-Level Chemistry Paper 3, 2023: Question 30

Question

Most scientists believe that the concentration of ozone in the upper atmosphere should not be allowed to decrease.

Which statement is a correct reason for this belief?

• A: Ozone helps to prevent global warming.
• B: Ozone is an efficient disinfectant.
• C: Ozone helps to remove pollutants such as chloroalkanes.
• D: Ozone absorbs ultraviolet radiation.

Correct Answer: D

Ozone absorbs ultraviolet radiation.

Explanation

Ozone (O₃) in the stratosphere plays a critical role in absorbing harmful ultraviolet (UV) radiation from the Sun. Without this protective layer, UV radiation would reach Earth's surface at much higher levels, causing serious health issues such as skin cancer and cataracts, as well as harming ecosystems.

Here's why the other options are incorrect:

• A: While ozone has some effect on Earth's radiation balance, it is not a primary factor in preventing global warming. Greenhouse gases like carbon dioxide (CO₂) and methane (CH₄) play a larger role.
• B: Ozone can act as a disinfectant, but this property is not relevant to its role in the upper atmosphere.
• C: Ozone does not directly remove pollutants such as chloroalkanes. In fact, chloroalkanes contribute to ozone depletion.

Key Takeaway

The primary reason for preserving stratospheric ozone is its role in absorbing harmful UV radiation, ensuring life on Earth is protected from its damaging effects.