The formula of spine! structure is AB2 O4 . If A2+  and B 3+ just fit into the voids generated by the cubical-closest packing of O2- ions (r = 126 pm), the sizes of A 2+ and B 3+, respectively, are aboutThe compound BeO has zinc blende unit cell. If r(Be 2+) = 59 pm, r(0 2 -) = 126 pm and M(Be) = 9 g mor ‘, answer the following three questions

# The formula of spine! structure is AB2 O4 . If A2+  and B 3+ just fit into the voids generated by the cubical-closest packing of O2- ions (r = 126 pm), the sizes of A 2+ and B 3+, respectively, are aboutThe compound BeO has zinc blende unit cell. If r(Be 2+) = 59 pm, r(0 2 -) = 126 pm and M(Be) = 9 g mor ', answer the following three questions

1. A

52.3 pm, 28.4 pm

2. B

28.4 pm, 52.2 pm

3. C

89.1 pm, 72.7 pm

4. D

72.7 pm, 89.1 pm

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### Solution:

A2+ occupy tetrahedral voids and B 3+ occupy octahedral voids,

the sizes of A 2+ and B 3+,are  28.4 pm, 52.2 pm respectively

hence rA2+= 0.225 x 126 pm= 28.4 pm and rB3+= 0.414 x 126 pm= 52.2 pm  