Question

Number of triclinic crystal system among the following
Graphite, $ZnO$, $CdS$, $\left(PbC{O}_3\right)$, $HgS$ (cinnabar), $K_{2}C{r}_2{O}_7$, $CuS{O}_4.5H_{2}O$, $H_{3}B{O}_3$

Answer 1

In case of triclinic system, the axial distances are $a\ne b\ne c$ and the axial angles are $\alpha \ne \beta \ne \gamma$. The examples are $K_{2}C{r}_2{O}_7$, $CuS{O}_4.5H_{2}O$, $H_{3}B{O}_3$
Graphite, $ZnO$, $CdS$ and $HgS$ are hexagonal and $PbC{O}_3$ is orthorhombic.