The charge on a sulfide ion is -2. This is because sulfur, which is in group 16 of the periodic table, typically gains two electrons to achieve a stable electron configuration. When sulfur gains these two electrons, it forms a sulfide ion (S2-).
In its neutral state, sulfur has 16 electrons. By gaining two more electrons, it completes its outer shell, resembling the electron configuration of the noble gas argon. This results in a stable, negatively charged ion with a charge of -2.