The energy liberated on complete fission of 1 kg of ${ }_{92}{\mathrm{U}}^{235}$  is (Assume 200 MeV energy is liberated on fission of 1 nucleus)

Mass of a uranium nucleus
$\begin{array}{l}=92\times 1.6725\times {10}^{-27}+143\times 1.6747\times {10}^{-27}\\ =393.35\times {10}^{-27}\mathrm{kg}\end{array}$
Number of nuclei in the given mass
$=\frac{1}{393.35\times {10}^{-27}}=2.542\times {10}^{24}$
$\text{ Energy released }=200\times 2.542\times {10}^{24}\mathrm{MeV}$
$=5.08\times {10}^{26}\mathrm{MeV}=8.135\times {10}^{13}\mathrm{J}=8.2\times {10}^{13}\mathrm{J}$