For a crystal of sodium chloride, state :
The structural arrangement of the sodium chloride crystal.

Explanation

To describe the structural arrangement of a sodium chloride (NaCl) crystal, we can break down the information into clear steps:

### Step 1: Identify the Types of Ions
Sodium chloride consists of two types of ions: sodium ions (Na⁺) and chloride ions (Cl⁻).

### Step 2: Arrangement of Sodium Ions
In the NaCl crystal structure, sodium ions occupy the octahedral voids. These voids are located at:
- The edge centers of the cubic unit cell.
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