[A]: Plants growing under trees show less photosynthesis.
[R]: Green light is least effective in photosyn- thesis.

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 solve the question, we need to analyze both the assertion (A) and the reason (R) provided.

### Step 1: Understand the Assertion
The assertion states: "Plants growing under trees show less photosynthesis."
- This statement is true because plants that grow under trees receive less sunlight due to the shade created by the tree canopy. Since photosynthesis requires light, reduced light availability leads to lower rates of photosynthesis.

### Step 2: Understand the Reason
The reason states: "Green light is least effective in photosynthesis."
- This statement is also true. Chlorophyll, the green pigment in plants, reflects green light rather than absorbing it. Therefore, green light is not utilized effectively for photosynthesis, making it the least effective wavelength for this process.

### Step 3: Determine the Relationship Between A and R
Now we need to evaluate whether R is the correct explanation of A.
- Since the assertion is true (plants under trees do show less photosynthesis due to reduced light) and the reason is also true (green light is less effective for photosynthesis), we need to see if the reason explains the assertion. However, while both statements are true, the reason does not directly explain why plants under trees show less photosynthesis. The reduced light availability is due to shade, not specifically because of the effectiveness of green light.

### Conclusion
Given the analysis:
- Both A and R are true.
- However, R is not the correct explanation of A.

Thus, the correct option is: **If both A and R are true, R is not the correct explanation of A.**

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