Assertion: Biomagnification of DDT can enhance the decline in bird population.
Reason: DDT causes thinning of egg shell and their premature breaking by disturbing calcium metabolism.

Options

A. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).
B. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion, then mark (2).
C. If Assertion is true but Reason is false, then mark (3).
D. If both Assertion and Reason are false, then mark (4).

Answer

To solve the assertion and reason question regarding the impact of DDT on bird populations, we can break down the solution into clear steps:

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "Biomagnification of DDT can enhance the decline in bird population."
- Biomagnification refers to the process where the concentration of a substance, like DDT, increases in organisms at each successive trophic level in a food chain.

2. **Understanding the Reason**:
- The reason provided is that "DDT causes thinning of egg shells and their premature breaking by disturbing calcium metabolism."
- This means that DDT affects the reproductive success of birds by weakening their eggs, leading to higher rates of egg breakage and lower survival rates of chicks.

3. **Linking Assertion and Reason**:
- We need to determine if the reason explains the assertion.
- Since DDT accumulates in birds through biomagnification and subsequently causes eggshell thinning, which leads to a decline in bird populations, the reason directly supports the assertion.

4. **Evaluating Truthfulness**:
- Both the assertion and the reason are true statements based on scientific evidence regarding DDT's effects on wildlife.
- The assertion about biomagnification leading to a decline in bird populations is supported by the reason that explains how DDT causes eggshell thinning.

5. **Conclusion**:
- Since both the assertion and reason are true, and the reason correctly explains the assertion, the answer to the question is option 1: "Both assertion and reason are true, and reason is the correct explanation of the assertion."

### Final Answer:
**Option 1**: Both assertion and reason are true, and reason is the correct explanation of the assertion.

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