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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 magnesium ions, m and n, respectively, are (A) 1/2 , 1/8(B) 1 , 1/4(C) 1/2 , 1/2(D) 1/4 , 1/8 |
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Answer» Correct option is (A) 1/2 , 1/8 In ccp lattice: Number of O atoms → 4 Number of Octahedral voids → 4 Number of tatrahedral voids → 8 Number of Al3+ = 4 x m Number of Mg2+ = 8 x n Due to charge neutrality 4 (-2) + 4m (+3) + 8n (+2) = 0 ∴ m = 1/2 and n = 1/8 |
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