What is meant by mass defect?

What is pair production?

Calculate binding energy of oxygen nucleus $\left({}_8{}^{16}O\right)$ from the data given below:

Mass of a proton$=1.007825 \mathrm{u}$

Mass of a neutron$=1.008665 \mathrm{u}$

Mass of $\left({}_8{}^{16}O\right)=15.994915 \mathrm{u}$

$1 \mathrm{u}=1.6605\times {10}^{-27} \mathrm{kg}$