A chemical weed in troposphere and protectant in stratosphere is

Options

A. `CH_(4)`
B. `O_(3)`
C. CFC
D. `NO_(2)`

Answer

To solve the question "A chemical weed in troposphere and protectant in stratosphere is," we can follow these steps:

### Step 1: Understand the Terms
- **Weed in the troposphere**: This refers to a substance that is considered undesirable or harmful in the lower atmosphere (troposphere).
- **Protectant in the stratosphere**: This refers to a substance that provides protection against harmful elements, particularly UV radiation, in the upper atmosphere (stratosphere).

### Step 2: Identify the Layers of the Atmosphere
- The **troposphere** is the lowest layer of Earth's atmosphere where weather occurs and where pollutants can accumulate.
- The **stratosphere** is the layer above the troposphere, which contains the ozone layer that protects life on Earth from the sun's harmful ultraviolet (UV) radiation.

### Step 3: Analyze the Options
- **Methane**: A greenhouse gas but not a protectant in the stratosphere.
- **Ozone**: Acts as a pollutant in the troposphere and protects against UV radiation in the stratosphere.
- **Chlorofluorocarbon (CFC)**: Harmful to the ozone layer but does not act as a protectant.
- **Nitrogen dioxide**: An air pollutant but does not provide protection in the stratosphere.

### Step 4: Conclusion
- The only substance that fits both criteria (acting as a weed in the troposphere and a protectant in the stratosphere) is **ozone**. In the troposphere, it contributes to air pollution and is a greenhouse gas, while in the stratosphere, it forms the ozone layer that protects against UV radiation.

### Final Answer
The chemical weed in the troposphere and protectant in the stratosphere is **ozone**.

---