Final answer:
The correct ground-state electron configuration for the sulfide ion S²⁻ is 1s² 2s² 2p⁶ 3s² 3p⁶, as sulfur gains two electrons to fill its 3p orbital, making option (a) the answer.
Step-by-step explanation:
The ground-state electron configuration of the sulfide ion S²⁻ is 1s² 2s² 2p⁶ 3s² 3p⁶. This configuration is because sulfur normally has the electron configuration of 1s² 2s² 2p⁶ 3s² 3p⁴, and when it gains two electrons to form the sulfide ion, those additional electrons fill the 3p orbital. Therefore, option (a) is the correct answer: 1s² 2s² 2p⁶ 3s² 3p⁶.