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).

Answer 2

This is an assertion-reason question about nuclear fission and fusion. Instead of analyzing the assertion and reason in isolation, let's test each of the four given options directly to see which one fits the facts.

1. Option A (Both A and R true, R is the correct explanation of A): This would require Reason (R)'s claim — that binding energy per nucleon increases with increasing atomic number \( Z \) for heavy nuclei and decreases with increasing \( Z \) for light nuclei — to be factually accurate. The actual binding-energy-per-nucleon curve rises from light nuclei up to a maximum near iron (mass number around 56) and then falls for heavier nuclei, exactly the opposite trend to what Reason (R) describes. So this option is ruled out.
2. Option B (Both true, R not the correct explanation): This option also requires R to be true, which fails for the same reason as above; R misstates the direction of the binding-energy trend. Ruled out.
3. Option C (A true, R false): Checking Assertion (A) independently: heavy nuclei splitting apart (fission) and light nuclei combining (fusion) both move the resulting nuclei toward the peak of the binding-energy curve, so binding energy per nucleon increases in each case and the excess appears as released energy. This is a well-established fact, so A holds. Checking Reason (R): as shown above, it reverses the actual trend of the binding-energy curve, so R is false. This combination, A true and R false, matches what is expected.
4. Option D (Both false): This requires Assertion (A) itself to be false, but fission and fusion releasing energy is a directly verifiable physical fact, it is how nuclear reactors and stars produce energy, so A cannot be false. Ruled out.

Only option C survives this check: the assertion correctly describes energy release in fission and fusion, while the reason misdescribes the shape of the binding-energy-per-nucleon curve.

Therefore, the correct answer is Assertion (A) is true, but Reason (R) is false.