The mass of a ${ }_3^{7}Li$ nucleus is 0.042 amu less than the sum of the masses of all its nucleons. The binding energy per nucleon of ${ }_3^{7}Li$ nucleus is nearly     

For ${ }_3^{7}Li$ nucleus,

Mass defect, $\Delta m=0.042$ amu

$\because 1amu=931.5MeV/c^2$

$\therefore \Delta m=0.042\times 931.5MeV/c^2=39.1MeV/c^2$

Binding energy,

$E_{b,}=\Delta m{c}^2=\left(39.1\frac{MeV}{c^2}\right)c^2=39.1MeV$

Binding energy per nucleon, 

$E{\text{'}}_b=\frac{E_b}{A}=\frac{39.1MeV}{7}\approx 5.6MeV$