Question

The correct statement in the following is.

• A. The ionic crystal of $AgBr$ has Schottky defect
• B. The unit cell having crystal parameters, $a = b \neq c,$ $\alpha = \beta = 90^{o},\gamma = 120^{o}$ is hexagonal
• C. In ionic compounds having Frenkel defect the ratio $\frac{\gamma_{+}}{\gamma_{-}}$ is high
• D. The coordination number of $Na^{+}$ion in $NaCl$ is 4

Answer 1

Answer: (B)

The unit cell having crystal parameters, $a = b \neq c,$

$\alpha = \beta = 90^{o},\gamma = 120^{o}$ is hexagonal

Answer 2

A crystal system is hexagonal if its unit cell having $a = b \neq c$ axial ratio and $\alpha = \beta = 90{^\circ},$ $\gamma = 120{^\circ}$ axial angles.