JEE Advanced 2015 · Paper 1 · Chemistry Q38

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ChemistryMultiple correct+4 / -2Question 38 of 60

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

\dfrac12,\dfrac18

1,\dfrac14

\dfrac12,\dfrac12

\dfrac14,\dfrac18

Answer and worked solution

Official answer: A

Voids. A ccp array of N oxide ions has N octahedral and 2N tetrahedral voids.

Spinel MgAl₂O₄. With 4 O, 2 Al and 1 Mg:

$m=\frac24=\frac12$ of the octahedral voids;
$n=\frac18$ of the tetrahedral voids.

(A)

Topics:Crystal lattices and unit cells

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JEE Advanced 2015 · Paper 1, Chemistry question 38