What is the molecular formula for sulfur trioxide?

The correct molecular formula for sulfur trioxide is SO3. This nomenclature is derived from the systematic naming of compounds based on the number of atoms of each element present in the molecule. In this case, "trioxide" indicates that there are three oxygen atoms associated with one sulfur atom. The prefix "tri-" is used to denote the number three in naming compounds.

When constructing the molecular formula based on the name, it becomes clear that one sulfur (S) atom combines with three oxygen (O) atoms, which results in the formula SO3. This formula precisely reflects the composition indicated by the name "sulfur trioxide," adhering to the conventions of chemical nomenclature.

Other options do not align with the correct amounts of sulfur and oxygen presented in the name: SO2 indicates two oxygen atoms, S2O3 suggests two sulfur and three oxygen atoms (which is not representative of trioxide), and S3O2 suggests three sulfur and two oxygen atoms, none of which adhere to the description of sulfur trioxide. Thus, the correct answer is SO3.