Assertion (A): Energy is released when heavy nuclei undergo ...

CBSE Class 12 Physics 2026 All Sets Paper

Question : 13 of 16

Marks: +1, -0

Assertion (A): 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.

Both (A) and (R) are true and (R) is the correct explanation of (A).
Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
(A) is true but (R) is false.
(A) is false and (R) is true.

Solution:

Assertion: True. In fission (breaking heavy nuclei) and fusion (combining light nuclei), the product nuclei have a higher binding energy per nucleon than the initial nuclei. The decrease in mass (mass defect) is released as energy.
Reason: False. For heavy nuclei (A > 170), the binding energy per nucleon generally decreases as Z (or A) increases. For light nuclei, it increases with increasing Z until it reaches a maximum. The reason given incorrectly describes these trends.

Go to Question:

Prev Question

Next Question