What are the coordination number of `Na^+` and `Cl^-` ions in NaCl?

Explanation

Different steps involed in Born Haber cycle are as follows :
(i) Sublimation of sodium metal : `Na(s) to Na (g) , Delta_(sub)H^("ϴ") = 108.4 kj mol^(-1)`
(ii) Ionization of sodium atoms : `Na(g) to Na^(+)(g) + e^(-) (g), Delta_("ion")H^("ϴ")=496 kj mol^(-1)`
(iii) Dissociation of chlorine molecule : `""^(1//2) Cl_(2) (g) to Cl(g) , Delta_("bond") H^("ϴ")=121 kj mol^(-1)`
(iv) Electron gain enthalpy : `Cl(g) + e^(-) to Cl (g), Delta_("ion") H^("ϴ")=-348.6kj mol^(-1)`
(v) Formation of sodium chloride : `Na^(+) (g) + Cl (g) to to Na^(+) Cl^(-) (s)`
Applying Hess.s law, we get
`Delta_("lattice")H^("ϴ") = 411.2 + 108.4 + 121 + 496 - 348.6 , Delta_("lattice") H^("ϴ") = + 788 kj`