Final answer:
The statement is true; phosphorus forms a phosphide ion with a charge of -3 (P3-) when it gains three electrons.
Step-by-step explanation:
The statement that "Phosphide is the name of the anion formed when phosphorus gains three electrons" is true. When a phosphorus atom gains three electrons, it achieves an octet in its valence shell, which results in a charge of -3. The resulting anion is called a phosphide ion, abbreviated as P3-.
Similar to phosphorus, other nonmetals in group 15, like nitrogen, also form anions by gaining three electrons. Nitrogen forms a nitride ion with a charge of 3-, denoted as N3-. This process of forming anions is a way for nonmetals to achieve a stable electron configuration resembling that of the nearest noble gas.