What is the coordination number of Na+ and Cl– ions in NaCl lattice?

In the NaCl crystal lattice (rock salt structure), each Na+ ion is surrounded by 6 Cl– ions and each Cl– ion is surrounded by 6 Na+ ions in an octahedral arrangement. Therefore, the coordination number of both Na+ and Cl– is 6. This 6:6 coordination is characteristic of the face-centered cubic (FCC) arrangement of NaCl and is determined by the radius ratio (rNa+/rCl– ≈ 0.52), which falls in the range for octahedral coordination.