NaCl has fcc structure. Calculate the number of NaCl units in a unit cell of NaC

Number of Na+ ions in unit cell

Each edge of the cube is shared by four other cubes, so there is ¼ of a sodium ion at each edge.

There are four edges at the top, four at the bottom, and four at the bottom.

∴ Number of Na+ions=12edges×14lion1edge+1centre×1 ion1centre=3 ions + 1 ion=4 ions

There are four sodium ions in a unit cell of sodium chloride.