With decrease in water vapour content in air, velocity of sound

Options

A. increases
B. decreases
C. remains constant
D. either (a) or (b)

Explanation

To solve the question regarding the effect of decreasing water vapor content in air on the velocity of sound, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Relationship Between Density and Velocity of Sound**:
- The velocity of sound in a medium is influenced by the density of that medium. The general relationship is given by the formula:
\[ v = \sqrt{\frac{K}{\rho}} \]
where \( v \) is the velocity of sound, \( K \) is the bulk modulus of the medium, and \( \rho \) is the density of the medium.

2. **Effect of Water Vapor on Air Density**:
- Water vapor is less dense than dry air. When water vapor is present in the air, it replaces some of the heavier nitrogen and oxygen molecules, leading to a decrease in the overall density of the air.
- Therefore, when we decrease the water vapor content in the air, we are effectively increasing the density of the air.

3. **Analyzing the Change in Velocity**:
- Since the density of the air increases when water vapor is removed, we can analyze the effect on the velocity of sound.
- According to the relationship, if the density (\( \rho \)) increases, the velocity of sound (\( v \)) will decrease, because they are inversely related.

4. **Conclusion**:
- Thus, with a decrease in water vapor content in the air, the density of the air increases, leading to a decrease in the velocity of sound.

### Final Answer:
The velocity of sound will **decrease** with a decrease in water vapor content in the air.

---