Select number of molecules/ions in which central atom uses its $d_{z^{\mathit{2}}}$ orbital in hybridization.

${\mathrm{XeF}}_6,{ \mathrm{SOF}}_4,{ \mathrm{NO}}_3^{-},{ \mathrm{ClO}}_3^{-},{ \mathrm{BrF}}_3,{ \mathrm{IF}}_4^{-},{ \mathrm{COCl}}_2,{ \mathrm{PCl}}_6^{-}$

The hybridization of all the given molecule is,

${\mathrm{XeF}}_6\to s{p}^3{d}^2;{\mathrm{SOF}}_4\to s{p}^{3}d;{\mathrm{NO}}_3^{-}\to s{p}^2$

${\mathrm{ClO}}_3^{-}\to s{p}^3;{\mathrm{BrF}}_3\to s{p}^{3}d;{\mathrm{IF}}_4^{\ominus }\to s{p}^3{d}^2$

${\mathrm{COCl}}_2\to s{p}^2;{\mathrm{PCl}}_6^{-}\to s{p}^3{d}^2$

It is observed that in ${\mathrm{XeF}}_6\to s{p}^3{d}^2$, ${\mathrm{SOF}}_4\to s{p}^{3}d$, ${\mathrm{BrF}}_3\to s{p}^{3}d$, ${\mathrm{F}}_4^{\ominus }\to s{p}^3{d}^2$and ${\mathrm{PCl}}_6^{-}\to s{p}^3{d}^2$ there is usage of d orbital 

Hence, the number of molecules/ions in which the central atom uses its $d_{z^{\mathit{2}}}$ orbital in hybridization is 5.