Question

Which crystal system does $NaCl$ belong to?

• A. Hexagonal
• B. Cubic
• C. Tetragonal
• D. Orthorhombic

Answer 1

The correct option is B Cubic

The unit cell of $NaCl$ crystal is shown in the image attached. It is an FCC structure where the basis consists of one $Na$ atom and one $Cl$ atom separated by one half of the body diagonal of a unit cube. There are four formula units per cell. The positions are indicated by the coordinates shown in the figure.

$Na:0,0,0;\frac{1}{2}\frac{1}{2},0;\frac{1}{2},0,\frac{1}{2};0,\frac{1}{2},\frac{1}{2}$.

$Cl:\frac{1}{2},\frac{1}{2},\frac{1}{2};0,0,\frac{1}{2};0,\frac{1}{2},0;\frac{1}{2},0,0$.