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Activity 13.4 Class 10 Science

Activity 13.4: Ncert book Science class 10

Understanding Ozone Layer Depletion through Activity 13.4

This engaging activity, presented in Chapter 13 of the Class 10 NCERT Science book, aims to enhance our understanding of the chemicals responsible for the depletion of the ozone layer, the regulations to control these emissions, and the recent changes in the size of the ozone hole.

Materials Needed:

  • Access to a library, internet, or newspapers.


  1. Research: Visit your school’s library, use the internet, or refer to recent newspapers to gather information on chemicals that deplete the ozone layer.
  2. Identify Chemicals: Look for detailed reports or articles listing specific chemicals like Chlorofluorocarbons (CFCs) and other ozone-depleting substances (ODS).
  3. Analyze Regulations: Find out about international agreements or regulations like the Montreal Protocol aimed at reducing the emission of these harmful chemicals.
  4. Observe Changes: Look for scientific studies or news reports on the current state of the ozone layer and note if the size of the ozone hole has changed in recent years.


  • Chemicals Identified: Chlorofluorocarbons (CFCs), Halons, Carbon Tetrachloride, and Methyl Chloroform are among the primary culprits for ozone depletion.
  • Regulations and Protocols: The Montreal Protocol (1987) is a significant international agreement aimed at freezing and then reducing the production of CFCs and other ODS.
  • Current Status: Recent studies indicate that the measures to control ozone depletion have been effective, resulting in the gradual recovery of the ozone layer. The size of the ozone hole over Antarctica, for example, has shown signs of shrinking.

Explanation of Chemical Reactions:

Ozone ($O_3$) is formed when ultraviolet (UV) radiation splits an oxygen molecule ($O_2$) into two free oxygen atoms ($O$). These free atoms then combine with another oxygen molecule ($O_2$) to form ozone:
$$ O_2 \xrightarrow{\text{UV}} O + O $$
$$ O + O_2 \rightarrow O_3 $$

However, chemicals like CFCs break down in the stratosphere, releasing chlorine atoms that catalytically destroy ozone:
$$ \text{CCl}_2\text{F}_2 \xrightarrow{\text{UV}} \text{CClF}_2 + \text{Cl} $$
$$ \text{Cl} + O_3 \rightarrow \text{ClO} + O_2 $$
$$ \text{ClO} + O \rightarrow \text{Cl} + O_2 $$


This activity helps in understanding how human activities contribute to ozone layer depletion and the effectiveness of global efforts to counteract this damage. The recovery of the ozone layer highlights the success of international cooperation in environmental conservation.

Questions Based on the Activity:

What are CFCs?

Answer: Chlorofluorocarbons (CFCs) are synthetic compounds containing chlorine, fluorine, and carbon, used in refrigerants and aerosol propellants.

What role does the Montreal Protocol play in ozone layer protection?

Answer: The Montreal Protocol is an international treaty designed to phase out the production and consumption of ozone-depleting substances.

How does UV radiation contribute to the formation of ozone?

Answer: UV radiation splits molecular oxygen $({O_2})$ into free oxygen atoms $({O})$, which then combine with other oxygen molecules to form ozone $({O_3})$.

What is the impact of chlorine atoms on the ozone layer?

Answer: Chlorine atoms released from CFCs catalytically destroy ozone molecules, leading to the thinning of the ozone layer.

Has the size of the ozone hole changed recently?

Answer: Yes, studies indicate that the size of the ozone hole has been gradually shrinking due to the regulations limiting the emission of ozone-depleting substances.

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