1.

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

Answer»

`1/2, 1/8`
`1,1/4`
`1/2,1/2`
`1/4, 1/8`

Solution :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.]


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