Match List-I with List-II
| List-I | List-II | ||
|---|---|---|---|
| (Nuclear force/ Potential energy between two nucleons) | (Separation between two nucleons) | ||
| (A) | Saturation of nuclear forces at separation of______ between two nucleons | (I) | < 0.8 fm |
| (B) | Potential energy is minimum between two nucleons at separation between them equal to about | (II) | > 0.8 fm |
| (C) | Nuclear force between two nucleons is attractive for separation (distance) | (III) | 0.8 fm |
| (D) | Nuclear force between two nucleons is repulsive for separation (distance) | (IV) | > few fm |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A) - (IV), (B) - (III), (C) - (II), (D) - (I)
The nuclear force between two nucleons is attractive at moderate separations, repulsive closer than about 0.8 fm, and short-ranged, falling to nearly zero beyond a few femtometres.
(A) Saturation of nuclear forces at separation of______ between two nucleons — this matches (IV) > few fm. Beyond a few fm the force is negligible, so a nucleon interacts only with its nearest neighbours; this short range makes the force saturate.
(B) Potential energy is minimum between two nucleons at separation between them equal to about — this matches (III) 0.8 fm. The potential energy curve has its minimum here, where the force changes from repulsive to attractive.
(C) Nuclear force between two nucleons is attractive for separation (distance) — this matches (II) > 0.8 fm. Beyond the minimum the force pulls the nucleons together.
(D) Nuclear force between two nucleons is repulsive for separation (distance) — this matches (I) < 0.8 fm. Closer than the minimum the force pushes them apart.
Note: It seems that item (A) of the original NTA paper is loosely worded: saturation is not a force acting at a particular separation, but a result of the nuclear force becoming negligible beyond a few fm. The question can still be solved because (B), (C) and (D) each have only one possible match, and Option (1) is the only option containing all three.
NCERT (2026-27):
Nuclear Force – “… (ii) The nuclear force between two nucleons falls rapidly to zero as their distance is more than a few femtometres. This leads to saturation of forces in a medium or a large-sized nucleus, which is the reason for the constancy of the binding energy per nucleon.”
Nuclear Force – “… The potential energy is a minimum at a distance r0 of about 0.8 fm. This means that the force is attractive for distances larger than 0.8 fm and repulsive if they are separated by distances less than 0.8 fm.”
