The ozone layer forms naturally by:

Options

A. CFC with oxygen
B. UV radiation with oxygen
C. IR radiation with oxygen
D. oxygen and water vapour

Answer

### Step-by-Step Solution:

1. **Understanding Ozone**: Ozone (O₃) is a gas composed of three oxygen atoms. It is primarily found in the Earth's stratosphere, where it forms the ozone layer.

2. **Formation Process**: The formation of ozone occurs naturally in the atmosphere through a series of reactions involving ultraviolet (UV) radiation from the Sun.

3. **Dissociation of Oxygen**: The process begins when UV radiation dissociates molecular oxygen (O₂) into individual oxygen atoms (O). This can be represented as:
\[ \text{O}_2 \xrightarrow{\text{UV radiation}} 2 \text{O} \]

4. **Recombination to Form Ozone**: The free oxygen atoms (O) can then react with other oxygen molecules (O₂) in the presence of UV radiation to form ozone (O₃):
\[ \text{O} + \text{O}_2 \xrightarrow{\text{UV radiation}} \text{O}_3 \]

5. **Dynamic Equilibrium**: It is important to note that ozone is not only formed but can also be decomposed back into oxygen molecules and free oxygen atoms when exposed to UV radiation:
\[ \text{O}_3 \xrightarrow{\text{UV radiation}} \text{O}_2 + \text{O} \]
This means that there is a continuous cycle of creation and destruction of ozone in the atmosphere.

6. **Conclusion**: Therefore, the ozone layer forms naturally by the interaction of UV radiation with oxygen molecules, leading to the formation of ozone.

### Final Answer:
The ozone layer forms naturally by UV radiation interacting with oxygen.

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