Which is responsible mainly for depletion of ozone layer ?

Options

A. CFCS
B. HCFs
C. `CH_(3)Br`
D. all are correct.

Answer

### Step-by-Step Solution:

1. **Identify the Main Culprit**: The primary substances responsible for the depletion of the ozone layer are chlorofluorocarbons (CFCs).

2. **Understanding CFCs**: CFCs are chemical compounds that contain chlorine, fluorine, and carbon. One common example of a CFC is Freon, specifically CF2Cl2.

3. **Mechanism of Ozone Depletion**:
- When CFCs are released into the atmosphere, they eventually reach the stratosphere.
- In the presence of ultraviolet (UV) radiation from the sun, CFCs undergo photodissociation, breaking down into radicals. For example:
\[ \text{CF}_2\text{Cl}_2 \xrightarrow{\text{UV light}} \text{CF}_2\text{Cl} \cdot + \text{Cl} \cdot \]
- The chlorine radical (Cl·) produced is highly reactive and can interact with ozone (O3).

4. **Reaction with Ozone**:
- The chlorine radical reacts with ozone, leading to the destruction of ozone molecules:
\[ \text{Cl} \cdot + \text{O}_3 \rightarrow \text{ClO} \cdot + \text{O}_2 \]
- The chlorine monoxide radical (ClO·) can further react with nascent oxygen (O) to regenerate the chlorine radical:
\[ \text{ClO} \cdot + \text{O} \rightarrow \text{Cl} \cdot + \text{O}_2 \]
- This cycle can repeat, allowing a single chlorine atom to destroy thousands of ozone molecules.

5. **Conclusion**: The continuous release and breakdown of CFCs in the atmosphere lead to significant depletion of the ozone layer, which is crucial for protecting life on Earth from harmful UV radiation.