Explanation:
A sulfide ion S²⁻ is formed from sulfur atom.
An ion is an atom that has lost or gained electron.
Sulfur atom is made up of 16 electrons according to its position on the periodic table.
In essence, there are 16 negatively charged particles in an atom of sulfur.
Also, in the neutral or uncharged state, the number of electrons equals to the number of protons.
So, there are 16 electrons and protons in an atom of sulfur.
Charge = Number of protons - Number of electrons
Charge = 16 - 18 = -2