What is the formula for the phosphide ion?

The formula for the phosphide ion is represented as P³⁻, which indicates that phosphorus has gained three electrons. In its elemental form, phosphorus typically has five valence electrons. When it gains three additional electrons to achieve a full octet, it acquires a negative charge of three.

This charge is significant as it reflects the tendency of nonmetals, like phosphorus, to form anions in order to achieve a more stable electron configuration, akin to that of noble gases. The presence of three negative charges in P³⁻ plays an important role in chemical bonding, particularly in ionic compounds where phosphide ions bond with positively charged metal ions to form stable compounds.

The other options do not represent the correct charge for the phosphide ion based on the electron configuration and typical behavior of phosphorus in ionic bonding.