Heat of formation of –

 $\mathrm{MX}\left(\mathrm{\Delta H}\right)=-550\mathrm{kJ}{\mathrm{mol}}^{-1}$           

 Heat of sublimation of metal (M)

 = + 80 kJ mol^-1

Heat of dissociation of X₂ 

= 155 kJ mol^-1 

 Ionisation energy of M = 374 kJ mol^-1

 Electron gain enthalpy of X = -343 kJ mol^-1

The lattice enthalpy (in kJ mol^-1) of the salt MX(s) from the above data is