The correct answer to this question isphosphorus pentachloride. The P stands for Phosphorus, while the Cl represents chloride. The 5 means that there are 5 Cl atoms bonded to the Phosphorus atom, which represents the prefix Pentain the Pentachloride. The naming conventions for a molecular compound is based on the number of atoms.
Phosphorus Pentachloride is a colorless, water-sensitive, and moisture-sensitive solid, meaning it is water soluble. It was first created by an English chemist named Humphry Davy in 1808. His analysis was inaccurate, and thus a French chemist, Pierre Louis Dulong, revised Davy's analysis providing the first accurate analysis in 1816.