Which chemical formula corresponds to sulfur dioxide?

Sulfur dioxide is represented by the chemical formula ( \text{SO}_2 ). This formula indicates that each molecule of sulfur dioxide consists of one sulfur atom bonded to two oxygen atoms.

In naming this molecule, the prefix "di-" is used because there are two oxygen atoms present. The sulfur atom does not have a prefix because it is only one atom, and chemical nomenclature generally omits the "mono-" prefix for single atoms of the first element in a compound.

In contrast, the other choices represent different substances. ( \text{SO}_3 ) refers to sulfur trioxide, which has three oxygen atoms. ( \text{S}_2) could be misleading as it could represent a hypothetical compound with two sulfur atoms but does not conform to recognized nomenclature for sulfur oxides. Finally, ( \text{S}_4 ) suggests a compound with four sulfur atoms, which does not apply to any commonly known or stable oxide of sulfur. Therefore, the correct answer is ( \text{SO}_2 ), aligning perfectly with the nomenclature for sulfur dioxide specifically.