Question

Identify the system of crystal structure, if a = b $\ne$ c and $\alpha =\beta ={90}^{\circ }$ and $\gamma ={120}^{\circ }$

• A. Monoclinic
• B. Triclinic
• C. Hexagonal
• D. Rhombohedral

Answer 1

The correct option is C Hexagonal

In the hexagonal system, there is an axes with six-fold rotation symmetry. Just as in the trigonal system, if we chose this axis to be along the c direction, then we have $a=b\ne c$,$\alpha =\beta ={90}^{\circ }$, $\gamma ={120}^{\circ }$. There is only one lattice in the hexagonal system.

Hence, the correct option is $C$