The correct IUPAC nomenclature for K2O is D: dipotassium monoxide.
In this compound, there are two potassium (K) atoms and one oxygen (O) atom. According to IUPAC nomenclature, the prefix "di-" indicates two potassium atoms, and "mon-" indicates one oxygen atom.
While option A (potassium oxide) is a commonly used name, it does not follow the systematic IUPAC naming convention which specifies the number of each type of atom in the compound. Therefore, the most accurate answer is D.