Select the compounds which have polyatomic anion in their solid state?

An element would be one with a single atom. ${\mathrm{PCl}}_5$ is polyatomic since it includes two distinct elements, but since it is neutral, it is not an ion. P typically has a valence of 3, however it may also have a valence of 5+. When P and 5 chloride ions interact, P develops a 5+ charge.

$\text{ (a) }{\mathrm{PCl}}_5⟶{\mathrm{PCl}}_4^{+}+{\mathrm{PCl}}_6^{-}$

$\text{ (b) }{\mathrm{XeF}}_6⟶{\mathrm{XeF}}_5^{+}+{\mathrm{F}}^{-}$

$\text{ (c) }{\mathrm{BrF}}_3⟶{\mathrm{BrF}}_2^{+}+{\mathrm{BrF}}_4^{-}$

$\text{ (d) }{\mathrm{N}}_2{\mathrm{O}}_5⟶{\mathrm{NO}}_2^{+}+{\mathrm{NO}}_3^{-}$