Two nucleons are at a separation of $1 \mathrm{x} {10}^{-15}\mathrm{m}$ . The net force between them is ${\mathrm{F}}_1$, if both are neutrons; ${\mathrm{F}}_2$ if both are protons and ${\mathrm{F}}_3$ if one is a proton and other is a  neutron. In such a case

Nuclear forces are charge independent but there exists a repulsive force between two protons. Hence net attractive force between two proton is less than net attractive force between two neutrons or between a neutron and a proton.