Question

Two statements are given, one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer from the codes (A), (B), (C) and (D) as given below.
% Assertion Assertion (A): During the formation of a nucleus, the mass defect produced is the source of the binding energy of the nucleus.
Reason (R): For all nuclei, the value of binding energy per nucleon increases with mass number.

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

Hint:

The binding energy per nucleon increases with mass number for light nuclei, but it reaches a peak for medium-sized nuclei like iron. For heavier nuclei, the binding energy per nucleon decreases.

Answer 1

The Correct Option is C

- Assertion (A): The mass defect in the formation of a nucleus is indeed the source of the binding energy. The mass defect refers to the difference between the mass of the nucleus and the sum of the masses of the individual nucleons. This missing mass is converted into binding energy according to Einstein's equation \( E = \Delta m c^2 \). Therefore, Assertion (A) is true.
- Reason (R): The binding energy per nucleon does not continuously increase with mass number for all nuclei. While it does increase with mass number for light nuclei, it reaches a maximum value for medium
-sized nuclei (around iron
-56) and then decreases for heavier nuclei. Thus, Reason (R) is false because the binding energy per nucleon does not increase for all nuclei. Therefore, the correct answer is option (C): Assertion (A) is true, but Reason (R) is false.