Question

Assertion : Energy is released when heavy nuclei undergo fission or light nuclei undergo fusion. Reason (R): For heavy nuclei, binding energy per nucleon increases with increasing \( Z \) while for light nuclei, it decreases with increasing \( Z \).

• A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Both Assertion (A) and Reason (R) are false.

Hint:

Remember the binding energy curve:

Fusion releases energy for light nuclei
Fission releases energy for heavy nuclei
Maximum stability near iron

Answer 1

The Correct Option is C

Concept: The binding energy per nucleon curve explains nuclear stability:

Peaks around iron (\( A \approx 56 \))
Light nuclei gain stability by fusion
Heavy nuclei gain stability by fission

Step 1: Analyze Assertion (A).

Heavy nuclei (like uranium) split → higher binding energy per nucleon → energy released (fission)
Light nuclei (like hydrogen isotopes) combine → higher binding energy per nucleon → energy released (fusion)
Thus, Assertion is true.
Step 2: Analyze Reason (R). The reason claims:

Binding energy per nucleon increases with increasing \( Z \) for heavy nuclei
Decreases with increasing \( Z \) for light nuclei
This is incorrect. Actual trend:

Binding energy per nucleon increases with mass number up to iron
Then decreases for heavier nuclei
So the given reasoning is false.
Step 3: Conclusion.

Assertion → True
Reason → False
Hence, option (C).