[A]: Rate of transpiration is directly propor- tional to relative humidity.
[R]: Humid air increases rate of diffusion.

Options

A. If both A and R are true and R is the correct explanation of A
B. If both A and R are true but R is not the correct explanation of A
C. If A is true and R is false
D. If both A and R are false

Answer

To analyze the statements given in the question, we need to evaluate both the assertion [A] and the reason [R]:

### Step 1: Understanding Assertion [A]
The assertion states that "Rate of transpiration is directly proportional to relative humidity."

- **Explanation**: Transpiration is the process through which plants lose water vapor from their leaves through small openings called stomata. The rate of transpiration is influenced by several environmental factors, including relative humidity.

- **Evaluation**: In fact, the rate of transpiration is inversely proportional to relative humidity. When relative humidity is high, the external air contains more moisture, which reduces the gradient for water vapor to diffuse out of the leaf. Therefore, the assertion is **false**.

### Step 2: Understanding Reason [R]
The reason states that "Humid air increases the rate of diffusion."

- **Explanation**: Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration. In the context of transpiration, when the air is humid, there is less of a concentration gradient for water vapor to move from the leaf to the air.

- **Evaluation**: Therefore, humid air actually decreases the rate of diffusion of water vapor from the leaf to the atmosphere. Thus, the reason is also **false**.

### Conclusion
Both the assertion [A] and the reason [R] are false. The rate of transpiration is inversely proportional to relative humidity, and humid air does not increase the rate of diffusion; rather, dry air enhances the rate of diffusion.

### Final Answer
- Assertion [A]: False
- Reason [R]: False

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