Which one of the following does not increase the rate of diffusion?

Options

A. Decreasing the size of the molecules
B. Increasing the size of the molecules
C. Increasing the temperature of the fluid
D. Increasing the concentration of the molecule

Answer

To solve the question "Which one of the following does not increase the rate of diffusion?", we need to analyze each option provided and understand how they affect the rate of diffusion.

### Step-by-Step Solution:

1. **Understanding Diffusion**:
- Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration. It occurs in gases and liquids but is rare in solids due to the fixed positions of molecules in solids.

2. **Factors Affecting Diffusion**:
- The rate of diffusion is influenced by several factors:
- Concentration gradient: A higher concentration difference increases the rate of diffusion.
- Size of molecules: Smaller molecules diffuse faster than larger ones.
- Temperature: Higher temperatures increase the kinetic energy of molecules, leading to faster diffusion.
- Permeability of the membrane: A more permeable membrane allows for easier diffusion.

3. **Analyzing the Options**:
- **Option 1: Decreasing the size of the molecules**:
- Smaller molecules diffuse faster, so this option increases the rate of diffusion.
- **Option 2: Increasing the size of the molecules**:
- Larger molecules diffuse slower. Therefore, increasing the size of the molecules does not increase the rate of diffusion.
- **Option 3: Increasing the temperature of the fluid**:
- Higher temperatures increase molecular movement, thus increasing the rate of diffusion.
- **Option 4: Increasing the concentration of the molecule**:
- A higher concentration leads to a steeper concentration gradient, which increases the rate of diffusion.

4. **Conclusion**:
- The only option that does not increase the rate of diffusion is **Option 2: Increasing the size of the molecules**.

### Final Answer:
**Increasing the size of the molecules does not increase the rate of diffusion.**

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