Which statement is wrong about ozone layer ?

Options

A. Bad ozone formed in the lower atmosphere (troposhpere).
B. The thickness of ozone is measured in terms of dobson unit (DU)
C. Major ozone depleting substance is CFC.
D. Montreal protocol was signed at montreal (canada) in 1986 (effective in 1988)

Answer

To determine which statement is wrong about the ozone layer, we will analyze each of the provided statements one by one:

1. **Bad ozone is formed in the lower atmosphere (troposphere)**:
- This statement is **correct**. Ozone in the troposphere is considered "bad" ozone because it is a pollutant that can cause respiratory problems and other health issues. It is formed by chemical reactions between volatile organic compounds (VOCs) and nitrogen oxides in the presence of sunlight.

2. **The thickness of ozone is measured in terms of Dobson unit**:
- This statement is also **correct**. The Dobson unit (DU) is a unit of measurement used to quantify the amount of ozone in the atmosphere. One Dobson unit corresponds to a layer of ozone that would be 0.01 millimeters thick at standard temperature and pressure.

3. **Major ozone-depleting substance is CFC**:
- This statement is **correct**. Chlorofluorocarbons (CFCs) are indeed major ozone-depleting substances. They release chlorine atoms in the stratosphere, which catalyze the breakdown of ozone (O3) into oxygen (O2), leading to ozone depletion.

4. **The Montreal Protocol was signed in Montreal, Canada in 1986 and effective in 1988**:
- This statement is **incorrect**. The Montreal Protocol was actually signed on September 16, 1987, and it became effective on January 1, 1989. Therefore, this statement contains incorrect information regarding the dates.

Based on the analysis, the wrong statement about the ozone layer is the last one regarding the Montreal Protocol.

### Final Answer:
The wrong statement about the ozone layer is: "The Montreal Protocol was signed in Montreal, Canada in 1986 and effective in 1988."

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