What is the correct chemical formula for phosphorus pentachloride?

Phosphorus pentachloride is a compound that consists of one phosphorus atom bonded to five chlorine atoms. The naming convention "pentachloride" indicates that there are five chlorine atoms present in the molecule.

To derive the chemical formula from the name, we start with the prefix "penta-," which signifies five. Therefore, the formula must include one phosphorus atom (P) and five chlorine atoms (Cl). This leads to the formula PCl5, accurately representing one phosphorus atom combined with five chlorine atoms, which corresponds to the nomenclature used in chemistry.

In comparison, other options represent different compounds with fewer chlorine atoms. For example, PCl3 consists of three chlorine atoms, not five, and therefore does not match the description of phosphorus pentachloride. Similarly, PCl4 includes only four chlorine atoms, and PCl2 contains just two, which also do not fit the requirements indicated by the name of the compound. Thus, the correct formula for phosphorus pentachloride is indeed PCl5.