Assertion : Chloroplasta occur inside the leaves mostly in mesophyll cells along their walls.
Reason: The membrane system of chloroplast is responsible for trapping the light energy and also for the synthesis of ATP and NADPH.

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that chloroplasts are found mostly in the mesophyll cells of leaves along their walls. This is true because chloroplasts are organelles responsible for photosynthesis, and they are predominantly located in the mesophyll, which is the inner tissue of the leaf where light absorption occurs.

2. **Understanding the Reason**:
- The reason given is that the membrane system of chloroplasts is responsible for trapping light energy and synthesizing ATP and NADPH. This statement is also correct. The thylakoid membranes within chloroplasts contain chlorophyll, which captures light energy, and they facilitate the processes that convert this energy into chemical energy in the form of ATP and NADPH.

3. **Evaluating the Relationship**:
- While both the assertion and the reason are true, the reason does not directly explain the assertion. The assertion focuses on the location of chloroplasts in mesophyll cells, while the reason discusses the function of the chloroplasts. Thus, the reason does not provide a proper explanation for why chloroplasts are located in mesophyll cells.

4. **Conclusion**:
- Therefore, the assertion is true, and the reason is true, but the reason is not the correct explanation for the assertion.

### Final Answer:
- Assertion: True
- Reason: True
- Explanation: The reason is not the correct explanation for the assertion.

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