Question

Which of the following are the correct axial distances and axial angles for rhombohedral system?

• A. $a=b=c,\alpha =\beta =\gamma \ne {90}^{\circ }$
• B. $a=b\ne c,\alpha =\beta =\gamma ={90}^{\circ }$
• C. $a\ne b=c,\alpha =\beta =\gamma ={90}^{\circ }$
• D. $a\ne b\ne c,\alpha \ne \beta \ne \gamma \ne {90}^{\circ }$

Answer 1

The correct option is A $a=b=c,\alpha =\beta =\gamma \ne {90}^{\circ }$

The correct axial distances and axial angles for rhombohedral system are $a=b=c,\alpha =\beta =\gamma \ne {90}^{\circ }$.

All the three edge lengths are equal and all the three angles are equal but none of the angles is equal to ${90}^o$.

Examples of rhombohedral crystal include calcite, $NaN{O}_3$ and $CaC{O}_3$.

Hence, the correct option is $\text{A}$