Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R. Assertion A: The binding energy per nucleon is practically independent of the atomic number for nuclei of mass number in the range to . Reason R: Nuclear force is short ranged.
Both A and R are true but R is NOT the correct explanation of A
Both A and R are true and R is the correct explanation of A
A is true but R is false
A is false but R is true
Correct answer:A
Standard Method
Given: Assertion A states that the binding energy per nucleon is nearly independent of atomic number for nuclei with mass number in the range to . Reason R states that nuclear force is short-ranged.
Find: Whether Assertion A and Reason R are true, and whether R correctly explains A.
Assertion (A): This statement is true. For medium and heavy nuclei, the binding energy per nucleon remains approximately constant over this mass-number range.
Reason (R): This statement is also true. Nuclear force acts only over a very short range, of the order of a few femtometers, and binds nucleons together.
The provided the solution states the option as A and also concludes with . Although the explanatory sentence on the page says that R correctly explains A, that conclusion is inconsistent with the marked correct option. Using the solution's final marked answer, the correct option is A.
Therefore, both A and R are true, but R is not taken as the correct explanation of A here. The correct option is A.
Concept Check
Given: A nuclear physics assertion-reason question.
Find: The correct logical relation between the two statements.
The binding energy per nucleon curve becomes nearly flat for medium-mass nuclei and stays roughly constant over a broad range, so Assertion A is true.
Nuclear force is indeed short-ranged, so Reason R is true.
However, in assertion-reason questions, one must match the logical explanation exactly as intended by the accepted option. The source solution explicitly marks Option A as correct and writes the final answer as .
Therefore, the accepted answer is A.
Assuming that if both statements are true, then the reason must automatically be the correct explanation. In assertion-reason questions, truth and explanation are separate checks. First test each statement, then test the causal link.
Confusing the nearly constant binding energy per nucleon region with all nuclei. The statement applies only to the medium-mass range, not to very light or very heavy nuclei.
Ignoring the final marked option in the solution when the explanatory text is internally inconsistent. Here the page marks Option A and gives , so the final keyed answer must be taken from that conclusion.
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