Final answer:
The correct formula for the covalent compound phosphorus pentachloride is PCl₅, which corresponds to option c).
Step-by-step explanation:
The formula for the covalent compound with the name phosphorus pentachloride is PCl₅. This name indicates that there is one atom of phosphorus (P) and five atoms of chlorine (Cl) in each molecule. Covalent compounds are named using prefixes to indicate the number of each type of atom present. The 'penta-' prefix stands for five, so the correct answer is option c) PCl₅.