If the unit cell of a mineral has cubic close packed (ccp) array of oxygen atoms with m fraction of octahedral holes occupied by aluminium ions and n fraction of tetrahedral holes occupied by magnesiums ions, m and n respectively, are

Options

A. `1/2, 1/8`
B. `1,1/4`
C. `1/2,1/2`
D. `1/4, 1/8`

Answer

A

Explanation

c.c.p. is f.c.c. arrangement (z = 4) so number of `O^(2-)` ions are 4. Octahedral and tetrahedral holes are 4 and 8 respectively. As 8 negative changes can be neutralised by `2Al^(3+)` and `1Zn^(2+)` ion, m and n are `2/4=1/2` and `1/8` respectively.]