Correct option is B
Explanation-
In the crystalline structure of NaCl (which is a face-centered cubic lattice):
Each Na⁺ ion is octahedrally coordinated by 6 Cl⁻ ions.
Similarly, each Cl⁻ ion is also surrounded by 6 Na⁺ ions.
This gives both ions a coordination number of 6, which is a characteristic of the rock salt structure (the common structure of NaCl).
So, option 2 (Six) is the correct answer.
Incorrect options-
Option 1: Four
In tetrahedral coordination, an ion is surrounded by 4 oppositely charged ions. This occurs in structures like zinc blende (ZnS), not NaCl.
Option 3: Eight
In cesium chloride (CsCl) structure, the Cs⁺ ion is surrounded by 8 Cl⁻ ions in a body-centered cubic (bcc) arrangement.
This type of coordination occurs in compounds where the cation is much larger, like Cs⁺.
Option 4: Ten
A coordination number of 10 is very rare in ionic solids, especially for small ions like Na⁺.
This number would imply an extremely crowded environment, not feasible for Na⁺ in a stable crystal lattice.
