Which of the following pollutants will lead to the depletion of ozone layer?

Analysis

The question asks us to identify a specific pollutant responsible for the depletion of the ozone layer. The ozone layer ($O_3$) is a region in the stratosphere that protects the Earth from harmful ultraviolet (UV) radiation.

Concept Explanation

The depletion of the ozone layer is primarily caused by the release of chemicals that contain chlorine or bromine atoms. When these chemicals reach the stratosphere, they are broken down by UV radiation, releasing free radicals (such as chlorine atoms). These radicals act as catalysts in a chain reaction that breaks down ozone molecules into oxygen, effectively thinning the protective layer.

• Chlorofluorocarbons (CFCs): These are synthetic compounds formerly used in refrigerators, air conditioners, and aerosol sprays. They are chemically stable at the Earth's surface but decompose in the stratosphere to release chlorine atoms, which destroy ozone.
• Carbon(II) oxide ($CO$): This is a toxic gas produced by incomplete combustion. It is a major air pollutant but does not contribute to ozone depletion.
• Hydrogen sulphide ($H_2S$): This is a gas often associated with volcanic activity and decaying organic matter. It contributes to acid rain and air pollution but is not the primary cause of ozone depletion.
• Sulphur(IV) oxide ($SO_2$): This is a major contributor to acid rain, formed by burning fossil fuels containing sulphur. Like the others, it does not cause ozone depletion.

Step-by-Step Solution

1. Evaluate the options: We are looking for a substance that releases ozone-depleting substances (ODS) like chlorine into the stratosphere.
2. Identify the culprit: CFCs are the most well-known class of chemicals that cause ozone depletion. When a CFC molecule (e.g., $CFCl_3$) is exposed to UV light, it releases a chlorine atom ($Cl$).
3. The Reaction: The chlorine atom reacts with ozone ($O_3$): $Cl + O_3 \rightarrow ClO + O_2$ This reaction destroys the ozone molecule.
4. Conclusion: Among the given options, only chlorofluorocarbons have the chemical properties required to reach the stratosphere and catalyze the destruction of the ozone layer.

Correct Answer

The correct option is A.

Exam Tip

When you see "Ozone Depletion" in a Chemistry or Biology exam, immediately look for CFCs (Chlorofluorocarbons). If you see "Acid Rain," look for Sulphur(IV) oxide ($SO_2$) or Nitrogen(IV) oxide ($NO_2$). Remembering these associations will save you time in the exam hall!