If mass of  ${\mathrm{U}}^{235}$ = 235.12142 amu,mass of  ${\mathrm{U}}^{236}=$236.1205 amu and mass of neutron =1.008665 amu, then the energy required to remove one neutron from the nucleus ${\mathrm{U}}^{236}$ is nearly about:

Mass of one atom of ${\mathrm{U}}^{235}$

=235.121420 amu

Mass of one neutron = 1.008665 amu

Sum of the masses of ${\mathrm{U}}^{235}$ and neutron

= 236.130085 = 236.130 amu ${\mathrm{U}}^{236}$

Mass of one atom of 

= 236.123050 amu

= 236.123 amu

Increase in mass when one neutron is removed from 

${\mathrm{U}}^{236}$ = 236.136 - 236.123

 = 0.007 amu

$\therefore$  Energy required to remove one neutron

= 0.007 x 931 MeV

= 6.517 x MeV =6.5 MeV