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In corundum, oxide ions are arranged in ...

In corundum, oxide ions are arranged in hexagonal close packing and aluminium ionsa occpy tow-third of the octaheral voids. What is the formula of corrundum ? .

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Number of oxides per unit cell = 6
Number of octahedral voids per unit cell=6
Number of `Al^(+3)` ions in octahedral voids=`(6xx2)/3=4`
`therefore Al^(+3) : O^(-2)`
4 :6 or 2 :3
Hence, formula is `Al_2O_3`
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