Which of the following set of compounds/ions does not exist (under normal conditions)?

${\mathrm{XeF}}_3^{-},{\mathrm{ClI}}_3,{\mathrm{PBr}}_6^{-}$ set of the compound does not exist (under normal conditions). ${\mathrm{XeF}}_3^{-}\to$$\left(\text{ l. }p.\text{ at }{90}^{\circ }\right);{\mathrm{ClI}}_3$and ${\mathrm{PBr}}_6^{-}$(steric crowding).

Hence, option B is correct.