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JEE · NEET Previous Year Question

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

Topic: JEE PYQ

Answer: A. Full step-by-step solution below.

  1. A,
  2. B1,
  3. C,
  4. D,

Correct answer: A

Solution

(a) In ccp, O2– ions are 4.
Hence total negative charge = –8
Let Al3+ ions be x, and Mg2+ ions be y.
Total positve charge = 3x + 2y
⇒ 3x + 2y = 8
This relation is satisfied only by x = 2 and y = 1.
Hence number of Al3+ = 2.
and number of Mg2+ = 1.
n = fraction of octahedral holes occupied by Al3+ = =
and m = fraction of tetrahedral holes occupied by Mg2+ =
Hence, answer is (a)

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