A pair of nuclei for which $Z_{1}=N_{2}$ and $Z_{2}=N_{1}$ are called mirror isobars (the atomic and neutron numbers are interchanged). Binding-cnergy measurements on these nuclei can be used to obtain cvidence of the charge independence of nuclear forces (that is, proton-proton. proton-neutron, and neutron-neutron nuclear forces are equal). Calculate the difference in binding energy for the two mirror isobars 150 and 15 $\mathrm{N}$ . The electric repulsion among eight protons rather than seven accounts for the difference.