* Atomic Number: The number of protons in an atom defines its element. Sulfur's atomic number is 16, meaning a sulfur atom has 16 protons.
* Ions and Protons: Ions are formed by gaining or losing electrons, not protons. The charge on an ion tells you how many electrons have been gained or lost, but the number of protons remains the same.
* Sulfide Ion: The sulfide ion (S²⁻) has gained two electrons, but its number of protons remains 16.
Therefore, a sulfide ion (S²⁻) has 16 protons.
