If the nuclear force between two protons, two neutrons and between a proton and a neutron is denoted by Fpp, Fnn and Fpn, respectively, then, which of the following relations is correct?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Fpp = Fnn = Fpn
The nuclear force is charge independent: the strong attraction between two nucleons is (very nearly) the same whether they are two protons, two neutrons or a proton and a neutron. The Coulomb repulsion between two protons is a separate force and is not part of the nuclear force.
\( F_{pp} = F_{nn} = F_{pn} \)
Why the other options are incorrect
Option (1) Fpp > Fnn = Fpn — Incorrect. The charge of the proton does not make the nuclear force stronger; it adds a separate electrostatic repulsion.
Option (2) Fpp ≠ Fnn and Fpp = Fnp — Incorrect. The nuclear force between two protons is the same as between two neutrons.
Option (4) Fpp ≠ Fnn ≠ Fpn — Incorrect. All three nuclear forces are equal.
NCERT (2026-27):
Nuclear Force – “… (iii) The nuclear force between neutron-neutron, proton-neutron and proton-proton is approximately the same. The nuclear force does not depend on the electric charge.”