Which of the following statements regarding ozone is incorrect ?

Options

A. Good ozone' is formed in the lower atmosphere (troposphere) that absorbs harmful UV rays coming from Sun, 'bad ozone' is present in the upper part of atmosphere (stratosphere) that harms plants and animals.
B. The thickness of the ozone in a column of air from the ground to the top of the atmosphere is measured in terms of Dobson units (DU).
C. Recognising the deleterious effects of ozone depletion, an international treaty, known as the Montreal Protocol, was signed at Montreal (Canada) in 1987 (became effective in 1989) to control the emission of ozone depleting substances.
D. None of these

Answer

To determine which statement regarding ozone is incorrect, we will analyze each option provided in the question step by step.

### Step-by-Step Solution:

1. **Understanding Ozone**: Ozone (O3) is a molecule composed of three oxygen atoms. It exists in two primary layers of the atmosphere: the stratosphere and the troposphere.

2. **Analyzing the Statements**:
- **Statement 1**: "Good ozone is formed in lower atmosphere, troposphere that absorbs harmful UV rays coming from the sun. Bad ozone is present in the upper part of atmosphere, the stratosphere that harms plants and animals."
- This statement is incorrect. Ozone in the stratosphere (often referred to as "good ozone") protects life on Earth by absorbing harmful UV radiation. Ozone in the troposphere (often referred to as "bad ozone") is a pollutant that can harm human health and the environment.

- **Statement 2**: "Thickness of ozone in a column of air from the ground to top of the atmosphere is measured in terms of Dobson unit, Tu."
- This statement is correct. The thickness of the ozone layer is indeed measured in Dobson units.

- **Statement 3**: "Recognizing the deteriorating effect of ozone depletion, an international treaty known as Montreal Protocol was signed in Montreal, Canada in 1987 which became effective in 1989 to control emission of ozone-depleting substances."
- This statement is also correct. The Montreal Protocol was established to phase out substances that deplete the ozone layer.

- **Statement 4**: "None of these."
- This option suggests that all previous statements are correct, which is not the case.

3. **Conclusion**: Based on the analysis, the incorrect statement is **Statement 1**.

### Final Answer:
The incorrect statement regarding ozone is: "Good ozone is formed in lower atmosphere, troposphere that absorbs harmful UV rays coming from the sun. Bad ozone is present in the upper part of atmosphere, the stratosphere that harms plants and animals."

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