* Phosphorus (P) has an atomic number of 15, meaning it has 15 protons and 15 electrons.
* Noble gas configuration: Phosphorus wants to achieve the same electron configuration as the nearest noble gas, which is Argon (Ar). Argon has 18 electrons.
* Gaining electrons: To get to 18 electrons, phosphorus needs to gain 3 electrons.
* Charge: Gaining electrons gives the ion a negative charge. Since it gains 3 electrons, the charge is -3.
Therefore, the ion formed when phosphorus achieves a noble gas configuration is P³⁻ (phosphide ion).
