Question

for a certain crystal system the relation between edge lengths (a, b, and c) is
a = b = c
The relation between axial angles $\left(\alpha ,\beta \text{and}\gamma \right)$ is $\alpha =\beta =\gamma$
The pair of crystal system for which above relation holds true is:

• A. cubic and triclinic
• B. cubic and tetragonal
• C. hexagonal and orthorhombic
• D. cubic and rhombohedral

Answer 1

Answer: (D)

cubic and rhombohedral

The relation $a=b=c$ and $\alpha =\beta =\gamma$ holds for cubic and rhombohedral systems.

Cubic

$a=b=c$

$\alpha =\beta =\gamma ={90}^o$

Rhombohedral

$a=b=c$

$\alpha =\beta =\gamma \ne {90}^o$