Mark the correct statement from the following

Options

A. The ozone of stratosphere is a good ozone
B. Troposphere is on the top of stratosphere
C. The thickness of ozone is measured in Db
D. The wave length of UV-B is more than that of UV-A

Answer

To solve the question "Mark the correct statement from the following," we need to analyze each of the four statements provided and determine which one is accurate.

### Step-by-Step Solution:

1. **Analyze Statement 1: "The ozone of stratosphere is a good ozone."**
- The stratosphere, which extends from approximately 12 to 50 km above the Earth's surface, contains a significant amount of ozone. This ozone layer protects life on Earth by absorbing harmful ultraviolet (UV) radiation from the sun. Therefore, this statement is **correct**.

2. **Analyze Statement 2: "Troposphere is on the top of stratosphere."**
- The troposphere is the lowest layer of the Earth's atmosphere, extending from the surface up to about 12 km. The stratosphere lies above the troposphere, extending from about 12 km to 50 km. Thus, this statement is **incorrect**.

3. **Analyze Statement 3: "The thickness of ozone is measured in dB."**
- The thickness of the ozone layer is actually measured in Dobson Units (DU), not decibels (dB). Therefore, this statement is **incorrect**.

4. **Analyze Statement 4: "The wavelength of UV-B is more than that of UV-A."**
- UV rays are classified into three categories: UV-A (315-400 nm), UV-B (280-315 nm), and UV-C (100-280 nm). Since UV-A has a longer wavelength than UV-B, this statement is also **incorrect**.

### Conclusion:
The only correct statement among the four is:
- **The ozone of stratosphere is a good ozone.**

### Final Answer:
The correct statement is: **The ozone of stratosphere is a good ozone.**

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