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

In a Sodium Chloride (NaCl) crystal lattice, the ions are arranged in a Face-Centered Cubic (FCC) structure, also known as the rock salt structure. The coordination number refers to the number of nearest neighbors of an ion in the crystal.

• Each Na+ ion is located at the center of an octahedron and is surrounded by six Cl- ions at equal distances.
• Conversely, each Cl- ion is also surrounded by six Na+ ions in an octahedral geometry.

Because both the cation (Na+) and the anion (Cl-) have six immediate neighbors of the opposite charge, the coordination number for both ions is 6. This 6:6 coordination ratio is a characteristic feature of the NaCl lattice, confirming that Option C is correct.