question_answer

A crystal of formula \[\mathbf{A}{{\mathbf{B}}_{\mathbf{3}}}\] 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

Correct Answer: C

Solution :

     \[\frac{Co-ordination\,no\,of\,cation}{Co-ordination\,no\,of\,anion}\,=\frac{ch\arg e\,of\,cation}{ch\arg e\,of\,anion}\]             \[=\frac{3}{1}=3\] Now Co-ordination no. of A is as shown so of B is 2.