Question

A crystal of formula $A^{}{B}_3$ has $A$ ions at the cube corners and $B$ ions at the edge centers. The coordination numbers of $A$ and $B$ are, respectively :

• A. $6$ and $6$
• B. $2$ and $6$
• C. $6$ and $2$
• D. $8$ and $8$

Answer 1

The correct option is C $6$ and $2$

$A$ ions are situated at the corners. Each $A$ is surrounded by $6B$ ions situated at $6$ edge centers.

$B$ ions are surrounded by $2$ $A$ ions.

Hence, the coordination numbers of $A$ and $B$ are $6$ and $2$ respectively.