* Covalent bonds occur when atoms share electrons. This is typical of nonmetals bonding with each other.

* Ionic bonds occur when one atom (typically a metal) *transfers* an electron to another atom (typically a nonmetal). This creates positively and negatively charged ions that attract each other.

Let's look at each option:

* H2O (water): Hydrogen and oxygen are nonmetals and share electrons to form covalent bonds.

* SO2 (sulfur dioxide): Sulfur and oxygen are nonmetals and share electrons to form covalent bonds.

* K2O (potassium oxide): Potassium (K) is a metal, and oxygen (O) is a nonmetal. They form an ionic bond.

* PCl3 (phosphorus trichloride): Phosphorus and chlorine are nonmetals and share electrons to form covalent bonds.

Therefore, K2O is the only compound that does NOT have covalent bonds.