Lattice energy of crystal

The electrostatic attractive energy for $1$ mole of an ionic crystal is given by $E=-\dfrac{N_{o}Mz^{+}z^{-}e^2}{4\pi\epsilon_{o} R_{o}^2}$

Where $N_{o}$ denotes the Avogadro constant which is equal to $6.023\times 10^{23}$ , $M$ denotes the Madelung's constant , which depends on the geometry of the crystal, $z^{+}$ and $z^{-}$ denotes the charges on cations and anions respectively , $e$ denotes the electronic charge which is $1.6\times 10^{-19}$ coulombs and finally $R_{o}$ is the internuclear separation between the ions.

Plugging in all the values gives the answer as $\boxed{\approx 674~ \text{kJ mol}^{-1}}$ .