CBSE 2025, Set 2

Question

**Assertion (A):** The binding energy per nucleon is practically constant for mass number in the range $(30 < A < 170)$.

**Reason (R):** Nuclear forces between the nucleons for mass numbers in the range $(30 < A < 170)$ are not short-range. 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.

Edvaya · Accepted Answer

The correct answer is Assertion (A) is true, but Reason (R) is false.. **Step 1: Check Assertion (A)**
The binding energy curve demonstrates that the binding energy per nucleon (BE/A) is practically constant (around $8.0	ext{ MeV}$) for intermediate mass nuclei, i.e., $30 < A < 170$. (Assertion is **True**).

**Step 2: Check Reason (R)**
The strong nuclear force is inherently a **short-range force** (effective only up to $2$-$3	ext{ fm}$), regardless of the mass number of the nucleus. It is precisely *because* it is short-range that it shows the property of saturation, which in turn causes the BE/nucleon to be constant in that intermediate range. (Reason is **False**).

Thus, A is true, but R is false.

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