The increases in which of these properties doesn't increase the rate of diffusion of a gas across alveoli ?

Options

A. Solubility
B. Partial pressure gradient
C. Thickness of respiratory membrane
D. All of these

Answer

To solve the question regarding which property does not increase the rate of diffusion of a gas across the alveoli, we can analyze the properties mentioned:

1. **Solubility of the gas**: An increase in the solubility of a gas in blood enhances its ability to diffuse across the alveolar membrane. Therefore, higher solubility increases the rate of diffusion.

2. **Partial pressure gradient**: The partial pressure gradient is crucial for diffusion. A higher difference in partial pressure between the alveoli and the blood will drive more gas to diffuse. Thus, an increase in the partial pressure gradient also increases the rate of diffusion.

3. **Thickness of the respiratory membrane**: The thickness of the respiratory membrane is inversely related to the rate of diffusion. If the membrane is thicker, it takes longer for gases to diffuse through it. Therefore, an increase in the thickness of the respiratory membrane will decrease the rate of diffusion.

Based on this analysis, the property that does not increase the rate of diffusion of a gas across the alveoli is the **thickness of the respiratory membrane**.

### Step-by-Step Solution:
1. **Identify the properties affecting diffusion**: Understand the properties that influence the rate of diffusion, such as solubility, partial pressure gradient, and thickness of the membrane.

2. **Analyze each property**:
- **Solubility**: Higher solubility increases diffusion.
- **Partial Pressure Gradient**: A greater difference in pressure increases diffusion.
- **Thickness of the Membrane**: Increased thickness decreases diffusion.

3. **Determine the correct answer**: Since an increase in the thickness of the respiratory membrane decreases the rate of diffusion, this is the property that does not enhance diffusion.

### Final Answer:
The increase in the **thickness of the respiratory membrane** does not increase the rate of diffusion of a gas across the alveoli.