Which of the following is not a greenhouse gas?

Options

A. `CO_(2)`
B. `CH_(4)`
C. `C Cl_(2)F_(2)`
D. `O_(2)`

Answer

To determine which of the following is not a greenhouse gas, we will analyze each option provided:

1. **CO2 (Carbon Dioxide)**:
- Carbon dioxide is a well-known greenhouse gas that traps heat in the atmosphere. It is produced by natural processes such as respiration and volcanic eruptions, as well as human activities like burning fossil fuels.
- **Conclusion**: CO2 is a greenhouse gas.

2. **CH4 (Methane)**:
- Methane is another significant greenhouse gas, with a much higher heat-trapping ability than CO2, although it is present in smaller quantities. It is emitted during the production and transport of coal, oil, and natural gas, as well as from livestock and other agricultural practices.
- **Conclusion**: CH4 is a greenhouse gas.

3. **CCl2F2 (Dichlorodifluoromethane)**:
- This compound is a type of chlorofluorocarbon (CFC), which is known to contribute to the greenhouse effect. CFCs are man-made compounds that were commonly used in refrigeration and aerosol propellants.
- **Conclusion**: CCl2F2 is a greenhouse gas.

4. **O2 (Oxygen)**:
- Oxygen is essential for life on Earth and is not a greenhouse gas. It does not trap heat in the atmosphere and does not contribute to the greenhouse effect.
- **Conclusion**: O2 is not a greenhouse gas.

Based on the analysis, the answer to the question "Which of the following is not a greenhouse gas?" is **O2 (Oxygen)**.

### Final Answer:
**O2 (Oxygen) is not a greenhouse gas.**

---