"Grey Air" refers to

Options

A. Incomplete smog formation
B. `N_(2)O`
C. CO
D. `SO_(2)`

Answer

To answer the question "Grey Air" refers to, we will analyze the options provided and clarify the concept of grey air.

### Step-by-Step Solution:

1. **Understanding Grey Air**:
- Grey air is often associated with air pollution, specifically related to the presence of certain pollutants. It is commonly linked to photochemical smog, which is a type of air pollution.

2. **Identifying the Components of Grey Air**:
- Photochemical smog is primarily composed of ozone (O3) and peroxyacetyl nitrate (PAN). These components are formed when pollutants from vehicles and industrial emissions react in the presence of sunlight.

3. **Analyzing the Options**:
- **Option 1: Incomplete smoke formation**: This refers to the process where combustion does not fully convert fuel into carbon dioxide and water, leading to the release of various pollutants, including particulate matter and gases that contribute to grey air.
- **Option 2: N2O (Nitrous Oxide)**: While N2O is a greenhouse gas, it is not directly related to the formation of grey air.
- **Option 3: CO (Carbon Monoxide)**: CO is a pollutant but does not specifically define grey air.
- **Option 4: SO2 (Sulfur Dioxide)**: SO2 is a significant air pollutant but is more associated with acid rain rather than grey air.

4. **Conclusion**:
- Based on the analysis, grey air is best described by the process of incomplete smoke formation, which leads to the creation of photochemical smog. Therefore, the correct answer is **Option 1: Incomplete smoke formation**.

### Final Answer:
"Grey Air" refers to **incomplete smoke formation**.