Hybridization of phosphorus in the compound $\mathrm{xy}$ is : 

${\mathrm{PBr}}_5\left(s\right)+{\mathrm{Br}}_2\left(g\right)⟶xy\left(s\right)$ [$\mathrm{xy}$ = Ionic compound]

Hybridization of phosphorus in the compound $\mathrm{xy}$ is $s{p}^3$.

Given reaction,

${\mathrm{PBr}}_5\left(s\right)+{\mathrm{Br}}_2\left(g\right)⟶xy\left(s\right)$

The compound form the following reaction is, ⁣${\mathrm{PBr}}_7\left(s\right)$.

Phosphorus heptabromide  ${\mathrm{PBr}}_7\left(s\right)$ has $s{p}^3$ hybridization

Hence, the option D is correct.