Question

For a cubic crystal structure which one of the following relations indicating the cell characteristics is correct:
AIMPT -2007

• A. $a=b=c$ and $\alpha \ne \beta \ne \gamma ={90}^0$
• B. $a\ne b\ne c$ and $\alpha \ne \beta and\gamma \ne {90}^0$
• C. $a=b=c$ and $\alpha =\beta =\gamma ={90}^0$
• D. $a\ne b\ne c$ and $\alpha =\beta =\gamma ={90}^0$

Answer 1

The correct option is C $a=b=c$ and $\alpha =\beta =\gamma ={90}^0$

For 3D-space lattice, there are seven unique and basic unit-cell shapes (primitive unit cells) with varying elements of symmetry in a three-dimensional space.
Out of 7 crystal system, only cubic and rhombohedral has same length for all the sides.
Cubic crystal system:
$a=b=c;\alpha =\beta =\gamma ={90}^o$

$NaCl,ZnS$ and $Cu$ are examples of cubic crystals.