What are the constituents of air?

Answer

### Step-by-Step Solution:

1. **Understanding Air Composition**: Air is not a single substance but a mixture of various gases. The primary constituents of air need to be identified.

2. **Identifying Major Components**:
- **Nitrogen**: The largest component of air, making up approximately 78% of the total volume.
- **Oxygen**: The second most abundant gas, accounting for about 21% of air.

3. **Identifying Minor Components**:
- **Carbon Dioxide (CO₂)**: Present in trace amounts, typically around 0.04%.
- **Argon (Ar)**: A noble gas that constitutes about 0.93% of air.
- **Hydrogen (H₂)**: Found in very small quantities.
- **Water Vapor**: The amount can vary significantly depending on the humidity, but it is also present in trace amounts.

4. **Summary of Constituents**:
- The major constituents of air are:
- Nitrogen: 78%
- Oxygen: 21%
- The minor constituents include:
- Carbon Dioxide: ~0.04%
- Argon: ~0.93%
- Hydrogen: Trace amounts
- Water Vapor: Variable amounts

5. **Biological Relevance**:
- Oxygen is essential for human respiration.
- Carbon dioxide is utilized by plants during photosynthesis, while humans exhale carbon dioxide as a byproduct of respiration.