Q18. Binding energy of a certain nucleus is $18 \times 10 ^ { 8 } \mathrm {~J}$. How much is the difference between total mass of all the nucleons and nuclear mass of the given nucleus:\\
(1) $10 \mu \mathrm {~g}$\\
(2) $20 \mu \mathrm {~g}$\\
(3) $0.2 \mu \mathrm {~g}$\\
(4) $2 \mu \mathrm {~g}$