$M_p$ denotes the mass of a proton and $M_n$ that of a neutron. A given nucleus, of binding energy B, contains Z protons and N neutrons. The mass M(N, Z) of the nucleus is given by (c is the velocity of light)
Answer & explanation
Correct answer: option 3
$B=\left[Z M_p+N M_n-M(N, Z)\right] c^2$
$\Rightarrow M(M, Z)=Z M_p+N M_n-B / c^2$