Question

The formula of the spinel is ____________.

• A. $M{g}_{2}Al{O}_4$
• B. $MgA{l}_2{O}_4$
• C. $M{g}_{3}A{l}_2{O}_6$
• D. none of the above

Answer 1

Answer: (B)

$MgA{l}_2{O}_4$

As $O^{2-}$ ions forms ccp, spinel has $4$ negative ions in its structure. So, total positive charge should be $8$.
It has one $M{g}^{+2}$ ion occupying one-eight of the tetrahedral holes and $2$ $A{l}^{+3}$ ions occupying one-half of the octahedral holes. So, the compound is $MgA{l}_2{O}_4$.