Explanation

(a)
Difference between S and $S^{2 -}$is larger radii and larger size os $S^{2 -}$.
As the radii of the anion is always larger than the atomic radii of its parent atom. In an anion as electron or electrons are added to the neutral atom, the nuclear charge acts on more electrons, so that each electron is held less tightly and thereby, the electron cloud expands.