Which of the following is not a greenhouse gas ?

Options

A. CO
B. `O_(3)`
C. `CH_(4)`
D. `H_(2)O` vapour

Explanation

To determine which of the following is not a greenhouse gas, we need to first understand what greenhouse gases are and their role in the environment.

### Step-by-Step Solution:

1. **Definition of Greenhouse Gases**: Greenhouse gases are gases that absorb infrared radiation (heat) emitted from the Earth's surface. They trap heat in the atmosphere, contributing to the greenhouse effect and global warming.

2. **Common Greenhouse Gases**: Some common examples of greenhouse gases include:
- Carbon dioxide (CO2)
- Methane (CH4)
- Nitrous oxide (N2O)
- Water vapor (H2O)
- Ozone (O3)

3. **Identifying Non-Greenhouse Gases**: To find out which gas is not a greenhouse gas, we should look for gases that do not significantly absorb infrared radiation or do not contribute to the greenhouse effect.

4. **Analysis of Options**:
- **Carbon Dioxide (CO2)**: A well-known greenhouse gas.
- **Methane (CH4)**: Another potent greenhouse gas.
- **Ozone (O3)**: Acts as a greenhouse gas in the atmosphere.
- **Water Vapor (H2O)**: The most abundant greenhouse gas.
- **Carbon Monoxide (CO)**: While it is a toxic gas, it does not absorb significant infrared radiation and is not classified as a greenhouse gas.

5. **Conclusion**: Among the options provided, carbon monoxide (CO) is not a greenhouse gas. It is primarily known for its toxicity rather than its ability to contribute to the greenhouse effect.

### Final Answer:
The gas that is not a greenhouse gas is **Carbon Monoxide (CO)**.

---