Solid $PC{{l}_{5}}$ exist as:
A)$PC{{l}_{4}}^{+}$ and $PC{{l}_{6}}^{-}$
B)$PC{{l}_{3}}$ and $PC{{l}_{2}}$
C)$PC{{l}_{4}}$ and $PC{{l}_{8}}$
D)None of the above

Hint: The answer for this question can be approached on the basis of the fact that the phosphorus penta chloride always exists as ionic form having the opposite charges on it as this enhances the crystalline nature.

Complete answer:
We are familiar with the concepts of inorganic chemistry that deals with the facts about the structure of molecules according to various theories and also about in which form does that molecule exist.;
We shall now see the phosphorus penta chloride and its existence.
- Phosphorus pentachloride having the molecular formula$PC{{l}_{5}}$is one of the most important phosphorus chlorides which find the use as a chlorinating reagent.
- It is the colourless compound and also water sensitive and moisture sensitive solid and also the commercial samples can be yellowish in colour which is contaminated with hydrogen chloride.
- Phosphorus penta chloride is prepared by the chlorination process which involves chlorination of phosphorus trichloride.
- Because of the equilibrium of phosphorus penta chloride with that of phosphorus trichloride and chlorine, the samples of this compound that is$PC{{l}_{5}}$often contains chlorine and this imparts a greenish colouration.
- This phosphorus penta chloride has pungent smell in the solid state and it exists as ionic solid that is ${{[PC{{l}_{4}}]}^{+}}$${{[PC{{l}_{6}}]}^{-}}$ in which the cation is having tetrahedral geometry and anion is having the octahedral geometry.

Therefore, the correct answer is option A) $PC{{l}_{4}}^{+}$ and $PC{{l}_{6}}^{-}$

Note: Note that phosphorus pentachloride is having an irritating odour and it is decomposed by water to form hydrochloric acid and phosphoric acid and heat. This heat released is sufficient to ignite the surrounding combustible material and is corrosive to metals and tissues.