Question

$N{a}_{2}O$ has antifluorite structure. In $N{a}_{2}O,$ the coordination number of $N{a}^{+}\text{and}{O}^{2-}$ are, respectively:

Answer 1

$N{a}_{2}O$ has antifluorite type structure.
In this $O^{2-}$ ions forms the ccp arrangement, where, it occupies the corners and face centres of the cubic unit cell and $N{a}^{+}$ occupy all the tetrahedral voids of the fcc arrangements.
$N{a}^{+}$ at tetrahedral void are surrounded by 4 $O^{2-}$ ions and each $O^{2-}$ at corners are surrounded by 8 $N{a}^{+}$ ions.
Therefore,
The coordination number of $N{a}_{2}O$ in antifluorite structure is 4 : 8.