Assertion: The nuclear energy can be obtained by the nuclear fission of heavier nuclei as well as by fusion of lighter nuclei.
Reason: As the mass number increases, the binding energy per nucleon, first increases and then decreases.

Options

A. (a) If both Assertion and Reason are true and Reason is correct explanation of the Assertion.
B. (b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
C. (c) If Assertion is true, but the Reason is false.
D. (d) If Assertion is false but the Reason is true.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Assertion**: The assertion states that nuclear energy can be obtained from both nuclear fission of heavier nuclei and fusion of lighter nuclei.
- **Explanation**: In nuclear fission, a heavy nucleus splits into two or more smaller nuclei, releasing energy. In nuclear fusion, two light nuclei combine to form a heavier nucleus, also releasing energy.

2. **Understanding the Reason**: The reason provided states that as the mass number increases, the binding energy per nucleon first increases and then decreases.
- **Explanation**: The binding energy per nucleon is a measure of how tightly the nucleons (protons and neutrons) are held together in a nucleus. For lighter elements, the binding energy per nucleon increases with mass number, indicating more stability. However, after reaching a peak, for heavier elements, the binding energy per nucleon starts to decrease, indicating less stability.

3. **Analyzing the Relationship**: The assertion and reason are related. The assertion is true because both fission and fusion release energy due to changes in binding energy.
- **Explanation**: In fission, the binding energy per nucleon of the resulting smaller nuclei is greater than that of the original heavy nucleus, leading to energy release. In fusion, the binding energy per nucleon of the resulting heavier nucleus is greater than that of the original lighter nuclei, also leading to energy release.

4. **Conclusion**: Both the assertion and reason are true, and the reason correctly explains the assertion.
- **Final Statement**: Therefore, the correct answer is that both the assertion and reason are true, and the reason provides a correct explanation for the assertion.