Consider the following values for an ionic compound NaCl. 
$$\begin{gathered} {\mathrm{\Delta H}}_{\mathrm{f}}\left(\mathrm{NaCl}\right)=-200\mathrm{KJ}/\mathrm{mol};{\mathrm{\Delta H}}_{\text{sub }}\left(\mathrm{Na}\right(\mathrm{s}\left)\right)=650\mathrm{KJ}/\mathrm{mol};{\mathrm{\Delta H}}_{\mathrm{diss}}\left({\mathrm{Cl}}_2\left(\mathrm{g}\right)\right)=400\mathrm{KJ}/\mathrm{mol} \\ {\text{ I. E. }}_{\cdot }\left(\mathrm{Na}\right(\mathrm{g}\left)\right)=500\mathrm{kJ}/\mathrm{mol} \end{gathered}$$
Electron gain enthalpy (Cl(g)) = –350 KJ/mol Using Born Haber Cycle, The value of lattice energy is - U, the value of U is