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JEE Main 2025 Jan 23 Shift 2, Physics Q14: Mass-Energy and Nuclear Binding Energy

JEE Main2025Jan 23, Shift 2Physics
Q.

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 found to be practically independent of the atomic number , for nuclei with mass numbers between and .

Reason (R) : Nuclear force is long range.

In the light of the above statements, choose the correct answer from the options given below :

  1. A

    (A) is false but (R) is true

  2. B

    (A) is true but (R) is false

  3. C

    Both (A) and (R) are true and (R) is the correct explanation of (A)

  4. D

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

Solution

The binding-energy-per-nucleon curve has a broad flat plateau between roughly and at about MeV per nucleon. So Assertion (A) is true.

The reason for this saturation is precisely that nuclear forces are short-ranged: each nucleon interacts only with its nearest neighbours, so adding more nucleons (within the saturation regime) does not increase the per-nucleon binding. Long-range forces would in fact prevent saturation.

Hence Reason (R) is false (nuclear force is short range, not long range).

Concept behind this question

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