Question 4

In polar organic solvents, the fluorination of $PCl_5$ (using reagents like $AsF_3$ or $SbF_3$) involves the formation of ionic species. $PCl_5$ itself exists in equilibrium as $[PCl_4]^+[PCl_6]^-$ in such solvents. Upon partial fluorination, the chloride ions in the anions are substituted by fluoride ions, while the $[PCl_4]^+$ cation remains relatively stable. The reactions proceed as: $3PCl_5 + 2AsF_3 \rightarrow [PCl_4]^+[PCl_4F_2]^- + 2AsCl_3$ With more fluorinating agent: $PCl_5 + AsF_3 \rightarrow [PCl_4]^+[PF_6]^- + AsCl_3$ Thus, the species formed are $[PCl_4]^+[PCl_4F_2]^-$ and $[PCl_4]^+[PF_6]^-$. Correct option is (B).