In NaCl the centres of two nearest like-charged ions are present at a distance of:

Distance b/w two nearest Cl^-  $=\frac{\mathrm{a}}{\sqrt{2}}$
Distance b/w two nearest Na⁺$=\frac{\mathrm{a}}{\sqrt{2}}$

Na⁺ ions are at edge centres and at body centre.

Cl^- ions are at face centre and at corners