試題詳解

15. A mineral crystallizes in a cubic closest-packed array of oxygen ions (O²⁻) with aluminum ions (Al³⁺) in some of the octahedral holes and magnesium ions (Mg²⁺) in some of the tetrahedral holes. Which of the following statements about this compound is correct?
(A) The empirical formula is Al₂Mg₂O₅.
(B) Half of the octahedral holes are filled with aluminum ions.
(C) One-fourth of the tetrahedral holes are filled with magnesium ions.
(D) There are two oxygen ions in a unit cell.
(E) There are four aluminum ions in a unit cell.